To summarize the answers on the duplicate question: Should we allow questions regarding the Arabic language?
- There's an intersection between Islam and Arabic language, as all relevant sources of Islam are Arabic.
- A question can be regarded on-topic if it is asking about something related to Islam: For example Explanation of a meaning of a term from the perspective of Islam, explanation interpretation of specific words in a text.
- Grammatical, spelling and pronunciation related questions are more likely to be about Arabic language. In other words if the question is purely on Arabic language it is off-topic.
I'm aware that the grey zone here is pretty unclear and therefore the interpretation of many questions and whether they are on- or off-topic is somewhat opinion-based.
Now on your example:
How do I pronounce لا اله الا انت سبحانك
Yeah the question asks about a du'a, but it asks how to pronounce it and this is a question which is of the category purely Arabic language. Further as the site is digital and text based it is off-topic because we can't properly answer it within the limitation of the "Answer section". Pronunciation usually needs a verbal answer!
In the given case this question however would be much more answerable than other questions of the same category.
You could make such questions a bit more fitting by saying it is quranic du'a, but still you need an external link to a suitable answer (recitation), which in my opinion is an external answer! As pronunciation questions as already said can best be answered verbally by pronouncing it correctly. And from this perspective your answer post doesn't answer the given question at all.
But for the reasons I've addressed above, I'd suggest you to edit the question and make it suitable for the site and if it passes the peer-review for re-opening that would be nice.
Further the more we allow such grey zone questions the more we will be flooded with more purely Arabic language questions.
And just because the question might be off-topic this doesn't mean that we can't give a hint of an answer and this was done in my comment.
Further I've deleted my answer draft on the duplicate post:
I'd be glad if we can accept some reasonable amount of questions which are let's say more about Arabic but still related to Islam, but they should be answerable within the "answer post". I would rather support a new Arabic.SE site instead of accepting too much of its possible content, but actually the SE Team is no more supporting new site proposals as it seems.
Last, but not least, as stated in my comments on your post this site is supposed to be driven by community, so it is up to you guys to edit and re-phrase questions that are off-topic and try to make them suitable for this site. I've done this many times in the past as a regular user and I'm doing it from time to time now, but as a mod I've more focus on other topics and I can't handle everything going on, on the site all alone. We could close a lot questions less or close and re-open them faster if the community itself was more active. But that's sadly not the case: It is rather "you -> mods are closing ..." instead of "us -> community are supporting ... editing ...reviewing ...". We should work together instead of simply pushing everything or tasks (bad) on to others, moderators preferably. As I suppose that both moderators and community or let's say regular users have a common goal: making this site more useful and a better place for representing and discussing about Islam.