I have been learning English since I was in my secondary school.

I can speak "fluently", but sometimes I fouind my self in a situations where I can't mingle with others in social activities, and alsoin social settings as I didon't know what to talk about since they arsay. This is often because people talking about something that they are familiar with from their background as a "local" people (I live abroad now and I am still not familiar with their culture).

I wasalso sometimes hesitate as well to start a conversation, ask a question or even respond to others when they interact to me, not because I wasam afraid of making mistakes, it was more likbut more because I wasam worried if what I saidy will be culturally appropriate or not for them

I have been learning English since I was in my secondary school.

In a sentence like this, you don't need to have the 'my' as you are talking about being a part of secondary school in general, not your specific school!

I can speak "fluently" but sometimes I fouind my self in a situation where I can't mingle with others inat social activitiegatherings, and I also I didon't know what to talk about since they are talking about something thatwhich they are familiar with. Like their background as a "local" people. (I live abroad now and I am still not familiar with their culture).

I tried to leave this part mostly with the language you used as it's not *that* bad, but there's definitely some word choices / ways you could re-write the whole thing. Obviously this is going to depend not only on what English speaking country you are in, but also the regional dialect of that place. For example, this is how I (British) would completely re-write that.

"I can speak fluently but sometimes I find myself in a situation where I just can't mingle with others at social gatherings. Especially when they are talking about something either locally known or relating to their childhood, like a TV program or something that I just haven't learnt about by living here."

I took some liberties with your text, but I hope it's helpful!

I was also sometimes hesitate as wellant to start a conversation, ask a question or even respond to others when they interact to me, ned with me. Not because I was afraid of making mistakes, it was more like I was worried that if what I said willould be culturally appropriate or not for them.

This was generally okay! Just tidied it up a little and changed some words to ensure the tense remains the same.