In 3E, languages are turned into 1-dot merits and are no longer tied to Linguistics in any way (other than writing). You can learn four local languages instead of one of the big ones.
Which finally solves the silliness that learning your fifth language was much harder than learning your third, but also makes Language-learning charms somewhat redundant.
Strange Tongue Understanding is a Linguistics 3 Essence 1 reflexive 1 mote charm. You need to activate it for every complex sentence, or for every three or four simple sentences.
For the 8 XP it costs to learn this charm, you could learn three more directional languages or 12 local languages (at 9 XP), so often that'll be simpler given the size of Creation.
Fortunately, this charm can also be used to lower somebodies Guile by 1 by using extremely elaborate expressions, hiding your true intent in a statement. So it stays relevant even if you speak every language.
Mingled Tongue Technique (Linguistics 5 Essence 1) actually does more than let you speak or understand a language - for one scene, you can speak is a language that is understood by speakers of multiple languages at once. You reflexively spend 4m, 1wp and any two languages you know turn into a third language which is understood perfectly by everyone who speaks at least one of the base languages. You can add more languages for 3 motes each.
So yes, you can be the perfect interpreter and translator at Essence 1.
Single Voice Kata seems pretty pointless in the light of that. For 1 scene, 5m 1wp, you speak a language that is intuitively understood by everyone, but they can't answer you in the same language. Great if you ever run into anyone who does not speak any language you are familiar with, but that is pretty unlikely and it only allows one-way communication.
Excellent Emissary's Tongue is the "instant language learning" charm and needs Essence 3. As long as you keep 6 motes committed, you speak and understand one language. But you take a -3 penalty to social influence unless you have a week of practice. On the other hand, you learn the language for free after a season of having this charm committed.
@samdamandias , this is pretty much your Charm except it needs Linguistics 5 and 6 committed motes instead of just one. But it also comes with eventually learning the language