Communicating with Conjured Creatures

Question

This question seems to come up in every edition of D&D and this version does not seem to really clarify the situation.

All of the spells of the type Conjure X (Animals, Celestials, Elementals, Fey) have text of the form:

The summoned creature[s] are friendly to you and your companions... They obey any verbal commands that you issue to them.

There's no indication about languages, but then Conjure Animals allows you to summon lots of creatures that have no languages at all. So it's not clear the spells would work at all unless you were granted magic communication ability as part of the spell.

Is it safe to assume that communication with Conjured creatures is automatic?

Are there notes outside of the spell that may indicate the requirement to know some special language?

Answer 1

If the spell required you to share a language with the creature, it would say so.

Let's look at something like Modify Memory (PHB, page 261)

You must speak to the target to describe how it's memories are affected, and it must be able to understand your language for the modified memories to take root.

It's specifically called out that the target must be able to understand your language.
Command (PHB, page 223) is another example:

The spell has no effect if the target is undead, if it doesn’t understand your language, or if your command is directly harmful to it.

Since there is no mention of language in Conjure X's description, it will follow your commands regardless of the language you speak them in (although I think it would be a reasonable assumption that it has to be a known language within the DnD universe, not just one you made up on the spot).

Note though that the spell only says

they obey any verbal commands that you issue to them.

It doesn't allow you to automatically understand the creature's language, give the creature the ability to actually understand your language (unlike the Find Steed spell), or give it any special ability to communicate with you.
As per @SevenSidedDie's comment, they may not even understand the actual commands, being driven more so by magical impulse at the intent behind your words rather than by the words themselves.

Answer 2

Remember on page 4 one of the general principles of D&D 5e is that Specific beats General.

Remember this: If a specific rule contradicts a general rule, the specific rule wins.

The implication of this is as what Purple Monkey says. If the spell involving communication doesn't have a specific requirement about subject needing to know the same language as the caster then you can assume that the target understands the caster.