Command is an interesting #DnD spell. It may be the only one in the game that varies in power according to which language you're playing the game in.

In English, you're limited to unadorned intransitive verbs: "approach," "flee," "halt." But in Spanish, you can make pronouns part of an imperative verb: dámelo ("give it to me"), apuñálale ("stab him/her/em"), confésales ("confess to them").

In Russian, you can exploit the difference between perfective and imperfective verbs: повернись "turn around" (once) vs. поворачивась "turn around" (keep doing it).

The more agglutinative the language, the more specifics you can pack in there. If you speak a language that relies on particles, the more constrained you are.

I pity players who have to cast command in Chinese. Is 过来
"approach" a one-word command or a two-word command?

Which raises an interesting question: Assuming that the languages we speak as players and DMs are merely proxies for the languages characters speak in the game world (as per Lord of the Rings), who's to say that Common doesn't allow a pronoun to be affixed to a verb à la Spanish?

What kind of properties do different in-world languages have, and is command more powerful in some of them than others?

I would imagine that a language spoken by a long-lived folk with a hegemonic culture and a strong tradition of written lore would be very conservative.

In the linguistic sense, which is to say, continuing to preserve archaic pronunciation, vocabulary, inflection and sentence structure.

Whereas a short-lived race, or a group of loosely affiliated cultures that meet only to trade, might speak a particle-heavy creole.

Command would be much more powerful when cast using the former language than the latter, because so much more information could be packed into a single word.

Because English is such a thief of a language, the one thing we have going for us is that we can take advantage of our language's many synonyms, especially those that come from Latin and therefore have built-in adverbial affixes. We can't say "Come out!" but we can say "Emerge!"

Belated afterthought: None of the ones I know work this way, but there may exist languages that don't distinguish clearly between transitive and intransitive verbs, in which a verb might normally take an object, but if that same verb is used without one, an object is implied.

So if you said the equivalent of "Drop," for instance, it would be taken to mean "Drop [what you're holding]" and not "Drop [to the ground]." Or "Stab" might mean "Stab [the person next to you]" and not "Stab [ineffectually into the air]."