xgettext: add page (#3635)

pages/common/xgettext.md

@@ -0,0 +1,20 @@
+# xgettext
+
+> Extract gettext strings from code files.
+> More information: <https://www.gnu.org/software/gettext/manual/html_node/xgettext-Invocation.html>.
+
+- Scan file and output strings to `messages.po`:
+
+`xgettext {{path/to/input_file}}`
+
+- Use a different output filename:
+
+`xgettext --output {{path/to/output_file}} {{path/to/input_file}}`
+
+- Append new strings to an existing file:
+
+`xgettext --join-existing --output {{path/to/output_file}} {{path/to/input_file}}`
+
+- Don't add a header containing metadata to the output file:
+
+`xgettext --omit-header {{path/to/input_file}}`