Two years ago, H. S. Teoh presented a proof of concept for
[automatic extraction of gettext-style translation
strings](https://forum.dlang.org/post/[email protected]). I recently combined that idea with the existing [mofile](https://code.dlang.org/packages/mofile) package for reading translation tables in GNU gettext format, and the result is a feature rich solution for the support of multiple natural languages in D applications: https://code.dlang.org/packages/gettext. Perhaps not surprisingly, it can do more than GNU gettext itself.
I'd like to thank Steven Schveighoffer and Adam Ruppe for
[valuable forum
assistance](https://forum.dlang.org/post/[email protected]), and SARC B.V. for sponsoring. Some extracts from the [readme](https://github.com/veelo/gettext#readme) are included below:
# Features
- Concise translation markers that can be aliased to your
preference.
- All marked strings that are seen by the compiler are extracted
automatically.
- All (current and future) [D string literal
formats](https://dlang.org/spec/lex.html#string_literals) are
supported.
- Static initializers of fields, constants, immutables, manifest
constants and anonimous enums can be marked as translatable (a D
specialty).
- Concatenations of translatable strings, untranslated strings
and single chars are supported, even in initializers.
- Arrays of translatable strings are supported, also when
statically initialized.
- Plural forms are language dependent, and play nice with format
strings.
- Multiple identical strings are translated once, unless they are
given different contexts.
- Notes to the translator can be attached to individual
translatable strings.
- Code occurrences of strings are communicated to the translator.
- Available languages are discovered and selected at run-time.
- Platfom independent, not linked with C libraries.
- Automated generation of the translation table template.
- Automated merging into existing translations (requires [GNU
`gettext` utilities](https://www.gnu.org/software/gettext/)).
- Automated generation of binary translation tables (requires
[GNU `gettext` utilities](https://www.gnu.org/software/gettext/)).
- Includes utility for listing unmarked strings in the project.
# Usage
## Marking strings
Prepend `tr!` in front of every string literal that needs to be
translated. For instance:
```d
writeln(tr!"This string is to be translated");
writeln("This string will remain untranslated.");
```
## Plural forms
Sentences that should change in plural form depending on a number
should supply both singlular and plural forms with the number
like this:
```d
// Before:
writefln("%d green bottle(s) hanging on the wall", n);
// After:
writeln(tr!("one green bottle hanging on the wall",
"%d green bottles hanging on the wall")(n));
```
Note that the format specifier (`%d`, or `%s`, etc.) is optional
in the singular form.
Many languages have not just two forms like the English language
does, and translations in those languages can supply all the
forms that the particular language requires. This is handled by
the translator, and is demonstrated in [the example
below](https://github.com/veelo/gettext#example-1).
## Custom markers
If `tr` is too verbose for you, you can change it to whatever you
want:
```d
import gettext : _ = tr;
writeln(_!"No green bottles...");
```
## Marking format strings
Translatable strings can be format strings, used with
`std.format` and `std.stdio.writefln` etc. These format strings
do support plural forms, but the argument that determines the
form must be supplied to `tr` and not to `format`. The
corresponding format specifier will not be seen by `format` as it
will have been replaced with a string by `tr`. Example:
```d
format(tr!("Welcome %s, you may make a wish",
"Welcome %s, you may make %d wishes")(n), name);
```
The format specifier that selects the form is the last specifier
in the format string (here `%d`). In many sentences, however, the
specifier that should select the form cannot be the last. In
these cases, format specifiers must be given a position argument,
where the highest position determines the form:
```d
foreach (i, where; [tr!"hand", tr!"bush"])
format(tr!("One bird in the %1$s", "%2$d birds in the
%1$s")(i + 1), where);
```
Again, the specifier with the highest position argument will
never be seen by `format`. On a side note, some translations may
need a reordering of words, so translators may need to use
position arguments in their translated format strings anyway.
Note: Specifiers with and without a position argument must not be
mixed.
## Concatenations
Translators will be able to produce the best translations if they
get to work with full sentences, like
```d
auto message = format(tr!`Could not open the file "%s" for
reading.`, file);
```
However, in support of legacy code, concatenations of strings do
work:
```d
auto message = tr!`Could not open the file "` ~ file ~ tr!`" for
reading.`;
```
## Passing attributes
Optionally, two kinds of attributes can be passed to `tr`, in the
form of an associative array initializer. These are for passing
notes to the translator and for disambiguating identical
sentences with different meanings.
### Passing notes to the translator
Sometimes a sentence can be interpreted to mean different things,
and then it is important to be able to clarify things for the
translator. Here is an example of how to do this:
```d
auto name = tr!("Walter Bright", [Tr.note: "Proper name.
Phonetically: ˈwɔltər braɪt"]);
```
The GNU `gettext` manual has a section [about the translation of
proper
names](https://www.gnu.org/software/gettext/manual/html_node/Names.html).
### Disambiguate identical sentences
Multiple occurrences of the same sentence are combined into one
translation by default. In some cases, that may not work well.
Some language, for example, may need to translate identical menu
items in different menus differently. These can be disambiguated
by adding a context like so:
```d
auto labelOpenFile = tr!("Open", [Tr.context: "Menu|File"]);
auto labelOpenPrinter = tr!("Open", [Tr.context:
"Menu|File|Printer"]);
```
Notes and comments can be combined in any order:
```d
auto message1 = tr!("Review the draft.", [Tr.context:
"document"]);
auto message2 = tr!("Review the draft.", [Tr.context: "nautical",
Tr.note: `Nautical
term! "Draft" = how deep ` ~
`the bottom of
the ship is below ` ~
`the water
level.`]);
```
## Selecting a translation
Use the [following
functions](https://gettext.dpldocs.info/v1.0.1/gettext.html#function) to discover translation tables, get the language code for a table and activate a translation:
```d
string[] availableLanguages(string moPath = null)
string languageCode() @safe
string languageCode(string moFile) @safe
void selectLanguage(string moFile) @safe
```
Note that any translation that happens before a language is
selected, results in the value of the hard coded string.
# There's more
See the [full readme](https://github.com/veelo/gettext#readme)
for adding and updating translations, impact on footprint and
performance, limitations, and lots more.
Here's the result of two runs of one of the
[examples](https://github.com/veelo/gettext/tree/main/tests):
```
Hello! My name is Joe.
I'm counting one apple.
Hello! My name is Schmoe.
I'm counting 3 apples.
Hello! My name is Jane.
I'm counting 5 apples.
Hello! My name is Doe.
I'm counting 7 apples.
```
```
Привіт! Мене звати Joe.
Я рахую 1 яблуко.
Привіт! Мене звати Schmoe.
Я рахую 3 яблука.
Привіт! Мене звати Jane.
Я рахую 5 яблук.
Привіт! Мене звати Doe.
Я рахую 7 яблук.
```
Notice how the translation of "apple" in the last translation
changes with three different endings dependent on the number of
apples.
-- Bastiaan.
