This isn't a question of etiquette, it is a question of individual interpretation of the guidance of Ling SE "norms". There are no comments associated with the question that indicate a reason for closing: what you can know is that 5 people VTC'd, at least one person clicked the "Language-specific grammar" box, possibly the first person did so, and maybe all 5 agreed with that assessment.
There is no standardized or official guidance on what constitutes language-specific grammar, and no bright lines. Statistically-speaking, there are numerous strategies that might be followed to avoid this closure reason, which could increase the chances that some such question would survive. You should focus on the fact that linguistics is a general scientific discipline studying the nature of human language as a cognitive phenomenon, which ultimately means that we're devising a general theory of the language faculty. Language-learning mnemonics aimed at learning quirks of some language (the "CaReFuL" mnemonic for interpreting final consonants in French spelling) are not within the scope of linguistics. An understanding of rules of glide deletion and vocalization in Classical Arabic is within the scope of linguistics, and may (some possibility) have utility to the untrained language-learner.
Although this is not the logically most-obvious reason, the first problem is that it is addressed to a very small set of specialists within linguistics. I don't know what "ברוך הבא" says – I think the first letter is aleph, so questions like this don't even get a read from me. A first step to making the question more general is to transliterate the data. A second step is to shed illusions about literal meaning – why not just accept that "ברוך הבא" means "Welcome"? What do you really want to know? What does בָּא have to do with the question? It appears that your "real" question is about the historical source of this expression. As a linguistic matter, either this is a canned construction, or it is a productive construction just as "buys watercress" would be a freshly-constructed collocation in English. What are you really asking (we used to call that "unclear what you're asking").
A third problem is revealed in your suggestion that "the phrase literally means 'Blessed be the comer' instead of 'The comer is blessed'", which is that "ברוך הבא" means "רוך הבא", and strings like "Blessed be the comer" do not constitute the meaning of expressions in Hebrew, they are (possibly) a translation into English. And maybe (or maybe not) one translation into English better captures the meaning of some expression in some language better than a competing translation does. What real-word semantic difference do you think underlies the difference between 'Blessed be the comer' instead of 'The comer is blessed'?
I didn't extract anything that is about the language faculty from this discussion, but I can imagine ways in which the question could be narrowed to a more-linguistic topic, regarding language change, syntax and semantics.