Android UI framework

Question 1

I have found that there is an alternative solution : Android Bootstrap

It is not an "alternative solution". You still will need to be "working with Android layouts and make them adapt for all screen sizes", because Android Bootstrap does not change much related to that.

and provide nice UI components (buttons etc...)

It uses the same Android widget set that all other Android apps use.

is this kind of frameworks won't make the App runs slower ?

There is nothing in an Android Bootstrap project that would necessarily make the app significantly slower.

Is this only a UI framework like for the web (Bootstrap from twitter) ?

It is not even that. It is a starter project that demonstrates how to tie together a dozen or so open source libraries for Android app development. You can think of it as an extended version of the templates used to create new applications and activities in Eclipse or Android Studio.

This is not to say that Android Bootstrap is bad -- far from it. However, it does not resemble your description.

can we use with it everything in Android (Camera, micro etc...)

I have no idea what "micro" is with respect to Android. Since you are writing an Android application, just like any other Android application, you can use it with whatever parts of Android you choose to.

Can we include some Jars like Zbar ?

I see no reason why not.

Question 2

It is very common for such templating engines not to have exactly most components you need. for android it is basicallly about adding support third party libraries to get the exact experience you need. Thus you may want to consider adding more or lacking parts by leveraging some external libraries like those from HERE