msgcat: add page (#16912)

Co-authored-by: Managor <42655600+Managor@users.noreply.github.com>
Co-authored-by: Lena <126529524+acuteenvy@users.noreply.github.com>

pages/common/msgcat.md

@@ -0,0 +1,29 @@
+# msgcat
+
+> Concatenate and merge multiple `.po` translation files.
+> Useful in software localization pipelines to combine message catalogs with filtering options.
+> More information: <https://www.gnu.org/software/gettext/manual/html_node/msgcat-Invocation.html>.
+
+- Combine multiple `.po` files into one:
+
+`msgcat {{file1.po file2.po ...}} {{[-o|--output-file]}} {{combined.po}}`
+
+- Combine input files listed in a text file:
+
+`msgcat {{[-f|--files-from]}} {{path/to/file_list.txt}} {{[-o|--output-file]}} {{combined.po}}`
+
+- Set the output encoding (e.g. UTF-8):
+
+`msgcat {{[-t|--to-code]}} {{UTF-8}} {{input.po}} {{[-o|--output-file]}} {{output.po}}`
+
+- Output only unique messages (appearing in one file only):
+
+`msgcat {{[-u|--unique]}} {{file1.po file2.po ...}} {{[-o|--output-file]}} {{unique.po}}`
+
+- Use the first available translation for duplicate entries:
+
+`msgcat --use-first {{file1.po file2.po ...}} {{[-o|--output-file]}} {{output.po}}`
+
+- Display help:
+
+`msgcat {{[-h|--help]}}`