This distinction is not observed in MSA.I believe it means When we enter the mosque, we say a two-part prayer.
إن means if
إذا means when
The former is used when you are not sure whether the condition will be fulfilled. The latter is used when you know it will be fulfilled but are not sure when.
As far as MSA is concerned, they both mean both if and when. I don't know whether إذا is more common or not. Keep in mind thought, while this is general, it's not a rule. Some still make the distinction.If this distinction is no longer observed, what is the meaning of إذا in MSA? Does it mean if? If so, is it as common as, less common, or more common than إن in MSA?
I wouldn't count on that for knowing the intention. For most Arabic speakers, MSA and CA are one. Hence, if the speaker or writer knows the Classical distinction, he/she would make the distinction. I'm sure that the majority would not, but I'm quite confident that more people than one would think do make the distinction.snimmar: Is your sentence in MSA or CA? Otherwise we cannot tell what the author's intent was.
Just a side note. I wouldn't translate it this way, I doubt anyone would understand what is meant - be they Muslim or not, native Arabic speakers or not. It's up to you though.we say a two-part prayer