Output according to endpoints and nicer output with relations

Lets say, I have 3 tables:

Languages(id, locale) Pages(id,created_at,updated_at) PagesLang(id,page_id,language_id,title,content)

And I have to build API where, I can make query with enpoints like: ?fields=title,id,created_at ?pages_ids=1,2,3&fields=created_at

And app query from DB only required fields. I mean, if fields endpoint is only "created_at", it doesn't make query in PagesLang.

Second question - How to make output better, in format like:

page = [
    'title' =>  [ 
        'en' =>  "EN title", 
        'de' => "DE title"
    ],
    'id' => 1
] , 
 [
    'title' =>  [ 
        'en' =>  "EN title", 
        'de' => "DE title"
    ],
    'id' => 2
]

Maybe there is tools that somebody can share? or give some tips? :)