Sign lLanguage

She was upset and said that there are so many things to learn the same as learning another language and that she can't memorize them.

The friend didn't know of that funny incident, so I showed her a Youtube video of his.

The man fakes as if he werebeing a veteran sign language interpreter next to each famous person who speecheaks, and music is playing according to his hands' movements.

ThaIt was so funny that the friend and I couldn't stop laughing.

She was laughing and holding her stomach.

Probably the encouragement from me was a great successful.

When you have a hard time, please seewatch this Youtube video.

After work, I met a friend for the first time in half a year, and we chilled at a cafe.

Generally, you want to put a comma before conjunctions like "and" and "but" if they are introducing an independent clause (i.e. something that could stand as a sentence on its own).

She was upset and said that there are so many things to learn the same as learning another languagejust like learning another language, there are so many things to learn that she can't memorize them.

The way I understand it, "the same as learning another language" is describing "there are so many things to learn […] that she can't memorize them," so you shouldn't put in between the two parts.

The friend didn't know about that funny incident, so I showed a YoutTube video of hism.

We generally say "know about" when we're talking about topics in general, like "know about photosynthesis" or "know about chemistry." "A YouTube video of his" suggests that he uploaded the video, but that's not the case.

The man fakes the motions as if he were a veteran sign language interpreter next to each famous person who speecheaks, and music is playing according to his hands' movement.

There has to be an object that goes with "fake" as a verb; i.e. you must fake something.

I encouraged her to continue learning sign language more easily since there's a man who fakesand told her that she could do it, when there's a man who openly fakes knowledge of sign language openly in public in the world.

This is just my guess for what you mean, since I don't really read Japanese.

She was laughing so much she was holding her stomach.

Probably tThe encouragement from me was probably a great success.

Probably sounds more natural after the verb.

When you have a hard time, please see this Youtube video.

This is correct, but you have a typo. :)

After work, I met a friend for the first time in half a year, and we chilled at a cafe.

She was upset and said that there awere so many things to learn the same as learning another language that she can't memorize themat she couldn't memorize them, just like when one learns a foreign language.

The phrase "the same as learning another language" needs fit into the sentence a little differently. The other words I changed are less important but I think they sound more natural.

The friend didn't know that funny incident, so I showed a Youtube video of this.

The man fakes as if he were a veteran sign language interpreter next to each famous person who speecheaks, and music is playing according to his hands' movement.

ThaIt was so funny that themy friend and I couldn't stop laughing.

I encouraged her to continue learning sign language more easily since there's a mansince there are people who fakes sign language openly in public in the world.

I am not sure what you mean by "learn more easily" so I'm not sure I preserved the meaning of the sentence. If you write "in public" you don't need to write "openly."

ProbablyI think the encouragement from me was a great success.

Your original sentence is correct but sounds a little unnatural. You might also consider replacing "was a great success" with "worked."