Currently, the frontend en-GB.localise.php is a bit different in codestyle from the backend one.
This isn't an issue by itself, but since they are actually identical files otherwise, it makes sense to make the identical
Having them identical helps when translators use a translation tool (eg Crowdin) since the "Translation Memory" and duplicate string detection will then automatically "translate" the other file for them.
I just copied the backend file over to the frontend.
There is nothing really to test, code does the same before and after and since it works in backend, it will also work in frontend
Imho, it can be merged on review.