In latex (I am using LatexTools, if that’s relevant) the argument of some latex commands is flagged as a typo, for example the “1em” in \hspace{1em}. Even if I choose to ignore “1em”, it will still flag \hspace{2em} and so on.
Is it possible to teach the spell checker to ignore the arguments of certain commands?
The general way to accomplish something like that is to adjust the spelling_selector setting to tell it that it should not spell check certain things.
In this case, that would require that the syntax definition for Latex applies a specific scope to that text that you could use to adjust the setting.
I don’t use LaTeX myself, so I don’t know if that’s the case or not. One way to tell would be if the syntax highlighting can/does highlight that text differently than surrounding text; you can also put the cursor in it and use Tools > Developer > Show Scope Name and see if there’s anything in the listed scope that would distinguish that text from the surrounding text.
Unless you are willing to edit the scopes in the LaTeX language, unfortunately, I do not see a solution for this. Consider the two functions \title{} and \hspace{}. They have exactly the same scope meta.group.brace.latex. This implies that if you turn off the spell checker for one, you turn it off for the other.