I often encounter this problem myself, and see that other editors do too. Say, you can see an [[https://translatewiki.net/wiki/MediaWiki:Jade-bad-contentquality-value/en|English message]] which contains a variable written as ''$1''. In the Translate extension it is not clear what these ('') do represent: the very double quotation marks, or the markup to make a text italic. Thus, the translators often misinterpret those, and sometimes a //text like this// turns out to be a «text like this» (or vice versa) in the translation to a target language, or //**text like this**// turns out to be a **«text like this»**.
- [[https://translatewiki.net/w/i.php?title=MediaWiki:Jade-bad-contentquality-value/fr&oldid=8577852|Example of the previously linked English message translated into French]] or
- [[https://translatewiki.net/w/i.php?title=MediaWiki:Ow_searchnoresult/uk&oldid=4904424|This weird case of a message translated into Ukrainian]] (and [[https://translatewiki.net/w/i.php?title=MediaWiki:Ow_searchnoresult/uk&oldid=8583928|this is what it should look like]])
A way to fix this would be to separate the single quotation marks more, so that it would be clear that they're meant to make the text italic.
EDIT: I've also uploaded a file for a reference (this is from a Meta-wiki page named "User groups", the original English message is in italic, but that's not obvious for someone using the Translate extension: {F27876809}