The Imam usually leads prayer should also be accepted
the original sentence has 'msikitini' which means 'at the mosque' so I don't think you can leave that out. Unless you mean adding the article 'The', in which case, you're right
Where else would the Imam lead prayer? Unless if they are evacuating/exiled/the mosque got destroyed the Imam is most definitely will lead prayer in a Mosque.
If it's in the sentence, it's part of the translation
The English translation should be "The Iman usually leads prayer at the the mosque"
Missing one "The", which I think makes it very confusing. Reported