This section describes how to implement native language support in a program or library that is part of the PostgreSQL distribution. Currently, it only applies to C programs.
Adding NLS Support to a Program
Insert this code into the start-up sequence of the program:
(The progname can actually be chosen freely.)
Wherever a message that is a candidate for translation is found, a call to gettext() needs to be inserted. E.g.:
would be changed to:
(gettext is defined as a no-op if NLS support is not configured.)
This tends to add a lot of clutter. One common shortcut is to use:
Another solution is feasible if the program does much of its communication through one or a few functions, such as ereport() in the backend. Then you make this function call gettext internally on all input strings.
Add a file nls.mk in the directory with the program sources. This file will be read as a makefile. The following variable assignments need to be made here:CATALOG_NAME
The program name, as provided in the textdomain() call.AVAIL_LANGUAGES
List of provided translations — initially empty.GETTEXT_FILES
List of files that contain translatable strings, i.e., those marked with gettext or an alternative solution. Eventually, this will include nearly all source files of the program. If this list gets too long you can make the first “file” be a + and the second word be a file that contains one file name per line.GETTEXT_TRIGGERS
The tools that generate message catalogs for the translators to work on need to know what function calls contain translatable strings. By default, only gettext() calls are known. If you used _ or other identifiers you need to list them here. If the translatable string is not the first argument, the item needs to be of the form func:2 (for the second argument). If you have a function that supports pluralized messages, the item should look like func:1,2 (identifying the singular and plural message arguments).
The build system will automatically take care of building and installing the message catalogs.
Here are some guidelines for writing messages that are easily translatable.
Do not construct sentences at run-time, like:
The word order within the sentence might be different in other languages. Also, even if you remember to call gettext() on each fragment, the fragments might not translate well separately. It's better to duplicate a little code so that each message to be translated is a coherent whole. Only numbers, file names, and such-like run-time variables should be inserted at run time into a message text.
For similar reasons, this won't work:
because it assumes how the plural is formed. If you figured you could solve it like this:
then be disappointed. Some languages have more than two forms, with some peculiar rules. It's often best to design the message to avoid the issue altogether, for instance like this:
If you really want to construct a properly pluralized message, there is support for this, but it's a bit awkward. When generating a primary or detail error message in ereport(), you can write something like this:
The first argument is the format string appropriate for English singular form, the second is the format string appropriate for English plural form, and the third is the integer control value that determines which plural form to use. Subsequent arguments are formatted per the format string as usual. (Normally, the pluralization control value will also be one of the values to be formatted, so it has to be written twice.) In English it only matters whether n is 1 or not 1, but in other languages there can be many different plural forms. The translator sees the two English forms as a group and has the opportunity to supply multiple substitute strings, with the appropriate one being selected based on the run-time value of n.
If you need to pluralize a message that isn't going directly to an errmsg or errdetail report, you have to use the underlying function ngettext. See the gettext documentation.
If you want to communicate something to the translator, such as about how a message is intended to line up with other output, precede the occurrence of the string with a comment that starts with translator, e.g.:
These comments are copied to the message catalog files so that the translators can see them.
PostgreSQL programs (server and client) can issue their messages in your favorite language — if the messages have been translated. Creating and maintaining translated message sets needs the help of people who speak their own language well and want to contribute to the PostgreSQL effort. You do not have to be a programmer at all to do this. This section explains how to help.
We won't judge your language skills — this section is about software tools. Theoretically, you only need a text editor. But this is only in the unlikely event that you do not want to try out your translated messages. When you configure your source tree, be sure to use the --enable-nls option. This will also check for the libintl library and the msgfmt program, which all end users will need anyway. To try out your work, follow the applicable portions of the installation instructions.
If you want to start a new translation effort or want to do a message catalog merge (described later), you will need the programs xgettext and msgmerge, respectively, in a GNU-compatible implementation. Later, we will try to arrange it so that if you use a packaged source distribution, you won't need xgettext. (If working from Git, you will still need it.) GNU Gettext 0.10.36 or later is currently recommended.
Your local gettext implementation should come with its own documentation. Some of that is probably duplicated in what follows, but for additional details you should look there.
The pairs of original (English) messages and their (possibly) translated equivalents are kept in message catalogs, one for each program (although related programs can share a message catalog) and for each target language. There are two file formats for message catalogs: The first is the “PO” file (for Portable Object), which is a plain text file with special syntax that translators edit. The second is the “MO” file (for Machine Object), which is a binary file generated from the respective PO file and is used while the internationalized program is run. Translators do not deal with MO files; in fact hardly anyone does.
The extension of the message catalog file is to no surprise either .po or .mo. The base name is either the name of the program it accompanies, or the language the file is for, depending on the situation. This is a bit confusing. Examples are psql.po (PO file for psql) or fr.mo (MO file in French).
The file format of the PO files is illustrated here:
The msgid's are extracted from the program source. (They need not be, but this is the most common way.) The msgstr lines are initially empty and are filled in with useful strings by the translator. The strings can contain C-style escape characters and can be continued across lines as illustrated. (The next line must start at the beginning of the line.)
The # character introduces a comment. If whitespace immediately follows the # character, then this is a comment maintained by the translator. There can also be automatic comments, which have a non-whitespace character immediately following the #. These are maintained by the various tools that operate on the PO files and are intended to aid the translator.
The #. style comments are extracted from the source file where the message is used. Possibly the programmer has inserted information for the translator, such as about expected alignment. The #: comment indicates the exact location(s) where the message is used in the source. The translator need not look at the program source, but can if there is doubt about the correct translation. The #, comments contain flags that describe the message in some way. There are currently two flags: fuzzy is set if the message has possibly been outdated because of changes in the program source. The translator can then verify this and possibly remove the fuzzy flag. Note that fuzzy messages are not made available to the end user. The other flag is c-format, which indicates that the message is a printf-style format template. This means that the translation should also be a format string with the same number and type of placeholders. There are tools that can verify this, which key off the c-format flag.
OK, so how does one create a “blank” message catalog? First, go into the directory that contains the program whose messages you want to translate. If there is a file nls.mk, then this program has been prepared for translation.
If there are already some .po files, then someone has already done some translation work. The files are named language.po, where language is the ISO 639-1 two-letter language code (in lower case), e.g., fr.po for French. If there is really a need for more than one translation effort per language then the files can also be named language_region.po where region is the ISO 3166-1 two-letter country code (in upper case), e.g., pt_BR.po for Portuguese in Brazil. If you find the language you wanted you can just start working on that file.
If you need to start a new translation effort, then first run the command:
This will create a file progname.pot. (.pot to distinguish it from PO files that are “in production”. The T stands for “template”.) Copy this file to language.po and edit it. To make it known that the new language is available, also edit the file nls.mk and add the language (or language and country) code to the line that looks like:
(Other languages can appear, of course.)
As the underlying program or library changes, messages might be changed or added by the programmers. In this case you do not need to start from scratch. Instead, run the command:
which will create a new blank message catalog file (the pot file you started with) and will merge it with the existing PO files. If the merge algorithm is not sure about a particular message it marks it “fuzzy” as explained above. The new PO file is saved with a .po.new extension.
The PO files can be edited with a regular text editor. The translator should only change the area between the quotes after the msgstr directive, add comments, and alter the fuzzy flag. There is (unsurprisingly) a PO mode for Emacs, which I find quite useful.
The PO files need not be completely filled in. The software will automatically fall back to the original string if no translation (or an empty translation) is available. It is no problem to submit incomplete translations for inclusions in the source tree; that gives room for other people to pick up your work. However, you are encouraged to give priority to removing fuzzy entries after doing a merge. Remember that fuzzy entries will not be installed; they only serve as reference for what might be the right translation.
Here are some things to keep in mind while editing the translations:
Make sure that if the original ends with a newline, the translation does, too. Similarly for tabs, etc.
If the original is a printf format string, the translation also needs to be. The translation also needs to have the same format specifiers in the same order. Sometimes the natural rules of the language make this impossible or at least awkward. In that case you can modify the format specifiers like this:
Then the first placeholder will actually use the second argument from the list. The digits$ needs to follow the % immediately, before any other format manipulators. (This feature really exists in the printf family of functions. You might not have heard of it before because there is little use for it outside of message internationalization.)
If the original string contains a linguistic mistake, report that (or fix it yourself in the program source) and translate normally. The corrected string can be merged in when the program sources have been updated. If the original string contains a factual mistake, report that (or fix it yourself) and do not translate it. Instead, you can mark the string with a comment in the PO file.
Maintain the style and tone of the original string. Specifically, messages that are not sentences (cannot open file %s) should probably not start with a capital letter (if your language distinguishes letter case) or end with a period (if your language uses punctuation marks). It might help to read Section 53.3.
If you don't know what a message means, or if it is ambiguous, ask on the developers' mailing list. Chances are that English speaking end users might also not understand it or find it ambiguous, so it's best to improve the message.