hello guys, i was wondering if i wanna create mobile apps. What language should i learn ?
That depends, there are two major places in the mobile markt: android and ios. For android you need java, i recommend to start here to learn more, for ios you need swift. Windows phone i don't know, maybe c#? Someone else will have to answer that
what about phonehap this application allow you to create mobile apps with only HTML , CSS , JS
Is it safe to use? what i mean is there a lot of developer use it?
If you're planning to create games or heavy apps, phonegap will create an app for you with HTML, but it would lag a lot/very slow. It's best to code in native languages that @stetim94 listed.
That depends on what you want to build, phonegap will be able to do light things, for example a quiz (give the user random questions and let them submit answers), if you want something heavier, use the native language like @gaurangtandon says, i am right that windows phone apps are native c#? I am not 100% sure about it.
Like @ziadalian said i would reccomend http://phonegap.com/, you just need html/css/js . If you want to build specifically iphone apps swift2 (not swift) would be a great help: https://developer.apple.com/ios/?cid=wwa-us-kwg-features . And on the contrary if you want to build android app you need to know java