Infrastructure for supporting translations of plugins

manual/creating_plugins.rst

@@ -92,6 +92,11 @@ The first thing to note is that this zip file has a lot more files in it, explai
     **about.txt**
         A text file with information about the plugin
 
+    **translations**
+        A folder containing .mo files with the translations of the user
+        interface of your plugin into different languages. See below for
+        details.
+
 Now let's look at the code.
 
 __init__.py
@@ -175,6 +180,42 @@ You can see the ``prefs`` object being used in main.py:
 .. literalinclude:: plugin_examples/interface_demo/main.py
     :pyobject: DemoDialog.config
 
+Adding translations to your plugin
+--------------------------------------
+
+You can have all the user interface strings in your plugin translated and
+displayed in whatever language is set for the main calibre user interface.
+
+The first step is to go through your plugin's source code and mark all user
+visible strings as translatable, by surrounding them in _(). For example::
+
+    action_spec = (_('My plugin'), None, _('My plugin is cool'), None)
+
+Then use some program to generate .po files from your plugin source code. There
+should be one .po file for every language you want to translate into. For
+example: de.po for German, fr.po for French and so on. You can use the 
+`poedit <http://www.poedit.net/>`_ program for this.
+
+Send these .po files to your translators. Once you get them back, compile them
+into .mo files. You can again use poedit for that, or just do::
+
+    calibre-debug -c "from calibre.translations.msgfmt import main; main()" filename.po
+
+Put the .mo files into the ``translations`` folder in your plugin.
+
+The last step is to simply call the function `load_translations()` at the top
+of your plugin's .py files. For performance reasons you should only call this
+function in those .py files that actually have translatable strings. So in a
+typical User Interface plugin you would call it at the top of ``ui.py`` but not
+``__init__.py``.
+
+You can test the translations of your plugins by changing the user interface
+language in calibre under Preferences->Look & Feel or by running calibre like
+this::
+
+    CALIBRE_OVERRIDE_LANG=de calibre
+
+Replace ``de`` with the language code of the language you want to test.
 
 The plugin API
 --------------------------------

src/calibre/customize/zipplugin.py

@@ -81,6 +81,30 @@ def get_icons(zfp, name_or_list_of_names):
         ians = ians.pop(names[0])
     return ians
 
+_translations_cache = {}
+
+def load_translations(namespace, zfp):
+    null = object()
+    trans = _translations_cache.get(zfp, null)
+    if trans is None:
+        return
+    if trans is null:
+        from calibre.utils.localization import get_lang
+        lang = get_lang()
+        if not lang or lang == 'en':  # performance optimization
+            _translations_cache[zfp] = None
+            return
+        mo = get_resources(zfp, 'translations/%s.mo' % lang)
+        if mo is None:
+            _translations_cache[zfp] = None
+            return
+        from gettext import GNUTranslations
+        from io import BytesIO
+        trans = _translations_cache[zfp] = GNUTranslations(BytesIO(mo))
+
+    namespace['_'] = trans.gettext
+    namespace['ngettext'] = trans.ngettext
+
 class PluginLoader(object):
 
     def __init__(self):
@@ -147,11 +171,11 @@ class PluginLoader(object):
                 import_name), 'exec', dont_inherit=True)
             mod.__dict__['get_resources'] = partial(get_resources, zfp)
             mod.__dict__['get_icons'] = partial(get_icons, zfp)
+            mod.__dict__['load_translations'] = partial(load_translations, mod.__dict__, zfp)
             exec compiled in mod.__dict__
 
         return mod
 
-
     def load(self, path_to_zip_file):
         if not os.access(path_to_zip_file, os.R_OK):
             raise PluginNotFound('Cannot access %r'%path_to_zip_file)
@@ -193,7 +217,6 @@ class PluginLoader(object):
                 del self.loaded_plugins[plugin_name]
             raise
 
-
     def _locate_code(self, zf, path_to_zip_file):
         names = [x if isinstance(x, unicode) else x.decode('utf-8') for x in
                 zf.namelist()]

src/calibre/translations/msgfmt.py

@@ -143,7 +143,7 @@ def make(filename, outfile):
                     (infile, lno)
                 sys.exit(1)
             l = l[12:]
-            msgid += '\0' # separator of singular and plural
+            msgid += '\0'  # separator of singular and plural
             is_plural = True
         # Now we are in a msgstr section
         elif l.startswith('msgstr'):
@@ -155,7 +155,7 @@ def make(filename, outfile):
                     sys.exit(1)
                 l = l.split(']', 1)[1]
                 if msgstr:
-                    msgstr += '\0' # Separator of the various plural forms
+                    msgstr += '\0'  # Separator of the various plural forms
             else:
                 if is_plural:
                     print >> sys.stderr, 'indexed msgstr required for plural on  %s:%d' %\
@@ -184,7 +184,11 @@ def make(filename, outfile):
     # Compute output
     output = generate()
 
-    outfile.write(output)
+    try:
+        outfile.write(output)
+    except AttributeError:
+        with open(outfile, 'wb') as f:
+            f.write(output)
 
 
 def main():