The short answer is yes, questions about whether something sounds awkward/natural (and formal/informal) are on-topic here. These questions are hard to find answers to in dictionaries and other references, but easy for a fluent speaker to look at and say yes/no or natural/awkward.
I think that with a little bit of effort and thought, they can be made into a question that other learners can find more easily and that invites answers that have more explanation than just "yes it sounds OK".
This question is essentially a "Does this sound natural?" question:
"Whether" Vs. "If"
However, because it doesn't just ask 'Does "I don’t know whether this word fits in the sentence." sound natural?', it has an answer that is a really great discussion of how to use 'whether' and 'if' idiomatically that I think other learners can find when they're searching and that will really make it clear how to write their own sentences using 'whether' and 'if'.