Critter from The Book of Unwritten Tales speaks his own language but in many cases it's possible to understand what he is saying.

It is possible to have a conversation with a dog in dog language at the beginning of The Secret of Monkey Island. It's not all gibberish. He apparently tells you some plot points that are revealed later by other characters.

Vangers!

“Your task is to get some soft phlegma into your mechos as we need it in Podish.”

"The inevitable has occured! The eLeeches came to us. Take him and bring him to Podish, but remember: the eLeech is very fragile. Just when the Gulp-down starts, he'll die forever. Hurry up, charioteer!"

First that comes to mind is the language your write in.

But on a serious note, the cultist language Dark Wisdom (Domus Durbentia) in Blood. Not a full fledged language as only phrases have been released by Monolith but a language nonetheless.

Slightly off topic but I have been developing a language and its alphabet since I was 4. I even used it in one of my books.

"E sie paladin un Emon Atrep. E sie Riaklien Trientor!"

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Where does the strange language YOU invented come from?
It's really hard to decipher.

Big deal, that happens to me IRL every day.

http://conlang.wikia.com/wiki/Hymmnos from EXA_PICO (Ar tonelico and Surge Concerto).

I just remembered that No Man's Sky features alien languages. Four of them, [url=https://nomanssky.gamepedia.com/Category:Language]according to this wiki[/url]. The languages aren't fully developed and seems to be of the word switch variety (like English but with different words). The one peculiarity is that the words for the same thing changes based on how it is capitalised in English. For example: time = uzco, Time = Auers and TIME = Geiro in the Atlas language.

Are those games any good (either as games or language tutorials)? I've seen them come up a few times on Fanatical, but have hesitated to buy.

What, you've never seen the "I Can Has Cheezburger?" website? The LOLcats section is a great tutorial for Fairfox Style.

Final Fantasy X had Al Behd, fuill letters language in game you could find each and letter somewhere on a magazine and translate text in the game and in fuirther saves.

Many Zelda have Hylian language with symbols for letters i am sure.

Monster Hunter World has its own language for audio, not text iirc.

It means "I am a Paladin of Emon Atrep (High Fire). I am the Creeping Death".
I did not name the language. In the book the people of Disteryan speaks it. Also most spells and ancient writings alongside the puzzles are written/spoken in that language. The symbols are not latin tho. In its true form, it would look something like this.