Recently, I've been studying languages in person with others, and it made me feel fairly motivated.

You could leave out “in person” or “with others.” Either way would be fine. It’s not necessarily wrong to leave the sentence as it is, though.

I tried to stickreinforce grammar and vocabulary in my mind by only watching videos and reading.

It sounds like you were using videos and written works to get a feel for the language. “In my mind” is probably unnecessary, but I don’t think keeping it in hurts.

I realized, however, the importance of learning languages with others since I noticed a marked progress after speaking in my target language with others language learners.

The second use of “other” didn't need an s at the end.

Now, I think that learning languages not only helps me to do the things I love, but also makes me more sociable.

There were a couple of dropped s’s on the verbs.

Recently, I've been studying languages in person with others, and it's made me feel fairly motivated.

"I've been studying languages in person with others" feels just a tad bit off, but how I might prefer to phrase it depends on the particulars of how you're doing it.

I tried to stickretain grammar and vocabulary in my mind by only watching videos and reading.

If you mean you learned unknown grammar and vocabular from videos and reading, "learn" seems better, but I though "retain" felt me likely.

At that time, I was fairlytoo shy to ask others to study with me.

"Fairly" means "about right" or "very good", but here it looks like you mean to say your shyness was to such an extent that asking others to help was impossible. Thus, "too", meaning "surpassing the limit".

"This book is fairly difficult to read" -> You will struggle, but it's maybe not impossible.
"This book is too difficult to read" -> give up now

However, I realized, however, the importance of learning languages with others since Iafter noticeding a marked progress after speaking in my target language with others language learners.

LStudying language studys

I tried to stick to grammar and vocabulary in my mind by only watching videos and reading.

I tried to learn grammar and vocabulary by only watching videos and reading and then recite them in my mind.

I realized, however, the importance of learning languages with others, since I noticed a marked progress after speaking in my target language with others language learners.

This changed my attitude, and I started looking for people with whom to study with.

never end a sentence with a preposition

Now, I think that languages not only help me to do the things I love, but also make me more sociable.