Are these sentences correct?
The weather couldn't have been better to study languages.
The weather couldn't have been better to know new people in the world, thanks to the Italki.

(Could I use the word "weather" related with "circumstances, life situations, etc.."?)

Question

Are these sentences correct?
The weather couldn't have been better to study languages.
The weather couldn't have been better to know new people in the world, thanks to the Italki.

(Could I use the word "weather" related with "circumstances, life situations, etc.."?)

Answer

You could use the word “climate” in regard to general trends (economic and social) and abstract concepts.

The climate at the university was great for language learning,
The economic climate was not good for small business.

Answer

Your sentence doesn't sound natural but the meaning is clear.  This would be another way to say it:
"When the weather is nice it is easier to meet new people. Everybody is out enjoying the day and friendly."