Improve PO rules: Add check for square bracket count
Originally created by @emmapeel on #15454 (Redmine)
Our beautiful translators are human after all, and sometimes they don’t copy the ikiwiki syntax quite right.
A simple check could be added to make sure the source and target strings have the same amount of [ and ] characters.
Reasoning:
- If there is an error on the number of brackets, ikiwiki will build without errors but the interface will be broken.