l10n: add .gitattributes to simplify location filtering

To simplify the location filtering process for l10n contributors when
committing po/XX.po files, add the filter attributes for .po files to
the repository. This ensures all contributors automatically get the
same filter configuration without manual setup in .git/info/attributes.

Contributors still need to manually define the filter drivers using
git-config as documented in po/README.md.

Signed-off-by: Jiang Xin <worldhello.net@gmail.com>

Author: jiangxin

po/.gitattributes

@@ -0,0 +1,37 @@
+# Git Attributes for PO Files
+#
+# This file configures Git filters to automatically strip location information
+# from PO files when committing, producing cleaner diffs and saving repository
+# space.
+#
+# Two filter types are used:
+# 1. gettext-no-file-no-location: Strips both filenames and line numbers
+#    (e.g., removes "#: main.c:123" entirely)
+# 2. gettext-no-location: Preserves filenames but removes line numbers, which
+#    requires gettext 0.20 or higher
+#    (e.g., "#: main.c:123" becomes "#: main.c")
+#
+# See `po/README.md` for instructions on setting up the required filter drivers.
+
+# Default: Strip both filenames and locations for all .po files
+*.po	filter=gettext-no-file-no-location
+
+# Explicitly documented languages using the default filter
+# (These inherit the *.po rule above but are listed here for documentation)
+bg.po	filter=gettext-no-file-no-location
+de.po	filter=gettext-no-file-no-location
+es.po	filter=gettext-no-file-no-location
+fr.po	filter=gettext-no-file-no-location
+ga.po	filter=gettext-no-file-no-location
+ru.po	filter=gettext-no-file-no-location
+sv.po	filter=gettext-no-file-no-location
+tr.po	filter=gettext-no-file-no-location
+uk.po	filter=gettext-no-file-no-location
+vi.po	filter=gettext-no-file-no-location
+
+# Languages that preserve filenames but strip line numbers
+# (These override the *.po rule above with a different filter)
+ca.po	filter=gettext-no-location
+id.po	filter=gettext-no-location
+zh_CN.po	filter=gettext-no-location
+zh_TW.po	filter=gettext-no-location

po/README.md

@@ -166,23 +166,26 @@ and make a user-friendly patch for review.
 To save a location-less "po/XX.po" automatically in repository, you
 can:
 
-First define a new attribute for "po/XX.po" by appending the following
-line in ".git/info/attributes":
+First, check which filter is configured for your "po/XX.po" file:
 
 ```
-/po/XX.po filter=gettext-no-location
+git check-attr filter po/XX.po
 ```
 
-Then define the driver for the "gettext-no-location" clean filter to
-strip out both filenames and locations from the contents as follows:
+The filter configuration is defined in the "po/.gitattributes" file.
+
+Then define the driver for the filter. Most languages use the
+"gettext-no-file-no-location" clean filter, which strips out both filenames and
+locations from the comments. To set this up, run the following command:
 
 ```shell
-git config --global filter.gettext-no-location.clean \
+git config --global filter.gettext-no-file-no-location.clean \
            "msgcat --no-location -"
 ```
 
-For users who have gettext version 0.20 or higher, it is also possible
-to define a clean filter to preserve filenames but not locations:
+Some languages use the "gettext-no-location" clean filter, which preserves
+filenames but not locations. For these, install gettext version 0.20 or higher
+and setup the driver as below:
 
 ```shell
 git config --global filter.gettext-no-location.clean \