Google Translate API and automatic language detection

Question

I have the following three questions:

• I want to use the Google API to translate text. I know that Google pays separately for translation and discovery. Google translate also supports translation of two translation methods.

  i) By setting both the source and the target, as in https://www.googleapis.com/language/translate/v2?key=INSERT-YOUR-KEY& source = en & target = de & q = Hello% 20world & q = My% 20name% 20is% 20Jeff

  ii) Specifying only the target, where is the source that we automatically detect, for example https://www.googleapis.com/language/translate/v2?key=INSERT-YOUR-KEY& target = de & q = Hello% 20world

My question is: if I call the API, as in the second example, will I be charged for both detection and translation, or just for translation?

2. Is it more effective when you specify both the source and the target than when you are only the target, or are there any drawbacks to using the second method above?

3. How many words must be sent to the Google Translate API to reliably determine the language?

thanks