Which Service of Google Translate API Should i choose (Translation/Language Detection)

Which Service of Google Translate API Should i choose
(Translation/Language Detection)

As Google Translate API Pricing page said it will charge $20 for
translation and $20 for language detection. But now i am confuse that
which service should I choose.
My requirement is like if i add friend word than it will provide me its
noun and all in my specific language. Like this,
Friend – Friends ;
-noun
vän friend, pal, fancier, well-wisher, lover, loverboy
väninna girlfriend, friend
kamrat companion, comrade, pal, friend, butty, chum
bekant friend
kväkare quaker, friend
In example i have added English language word and it have translates it in
Swedish. Like this example my input language can be any kind and my output
language is also different. So should i use Language detection?
Can somebody explain the difference of this two services?