The spell Command states the following:
You speak a one-word command to a creature you can see within range. The target must succeed on a Wisdom saving throw or follow the command on its next turn. 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. […]
Therefore, one would not be able to naturally command beasts which don't speak any or at least not your language.
If I were to be under the effect of the spell Speak with Animals, however, would the beast then be able to understand me and therefore forced to follow the command? The spell doesn't say that it “understands my language“, but I can verbally communicate with it.
You gain the ability to comprehend and verbally communicate with beasts for the duration. The knowledge and awareness of many beasts is limited by their intelligence, but at minimum, beasts can give you information about nearby locations and monsters, including whatever they can perceive or have perceived within the past day. You might be able to persuade a beast to perform a small favor for you, at the DM's discretion.
Similar to that, the Great Old One Warlock's Awakened Mind feature states:
Starting at 1st level, your alien knowledge gives you
the ability to touch the minds of other creatures. You
can communicate telepathically with any creature you
can see within 30 feet of you. You don’t need to share
a language with the creature for it to understand your
telepathic utterances, but the creature must be able to
understand at least one language.
So this would specifically rule out beasts that don't naturally speak any language, but other beasts (that speak for example slyvan) would, whether or not I speak that language.
Also, can I use Awakened Mind with Command at all? The latter mentions “You speak a one-word command […]“, while Awakened Mind just allows communicating telepathically.
Thank you in advance!