I find myself tempted to make very small changes in the English instructions of that language course, where the excellent and fully understandable English is just slightly awkward. (For instance, the expression "mother tongue speaker" is perfectly clear in context, but
- if I had chosen that phrase I would have hyphenated "mother-tongue" to make clear its role as an adjectivial phrase (or technically an attributive-noun phrase, I guess) modifying "speaker", and
- I probably would have in any case chosen instead "native speaker" -- which may be more ambiguous but to native speakers of English is so well established that it is probably the clearest way of stating the concept.
I suppose I'm being overly cautious, and shouldn't need any encouragement (after nearly 5 years at en: !); we'll see what happens.