Do not fail workflow if sunshine.po doesn't exist

- Add proper keywords for boost::locale
- Minor documentation updates about localization

.github/workflows/localize.yml

@@ -9,6 +9,9 @@ on:
       - 'locale/sunshine.po'
   workflow_dispatch:
 
+env:
+  file: ./locale/sunshine.po
+
 jobs:
   localize:
     name: Update Localization
@@ -37,9 +40,20 @@ jobs:
 
     - name: Update Strings
       run: |
+        # first, try to remove existing file as xgettext does not remove unused translations
+        if [ -f "${{ env.file }}" ];
+        then
+            rm ${{ env.file }}
+            echo "new_file=false" >> $GITHUB_ENV
+        else
+            echo "new_file=true" >> $GITHUB_ENV
+        fi
+
+        # extract the new strings
         python ./scripts/_locale.py --extract
 
     - name: git diff
+      if: ${{ env.new_file == 'false' }}
       run: |
         # disable the pager
         git config --global pager.diff false
@@ -52,7 +66,8 @@ jobs:
         echo "git_diff=${OUTPUT}" >> $GITHUB_ENV
 
     - name: git reset
-      if: ${{ env.git_diff == '1	1	locale/sunshine.po' }}  # only run if more than 1 line changed
+      # only run if a single line changed (date/time) and file already existed
+      if: ${{ env.git_diff == '1	1	locale/sunshine.po' && env.new_file == 'false' }}
       run: |
         git reset --hard