Question

If i have a JSON with phrases in different languages:

var lang = {
    'topic' : {
        'en' : 'Topic',
        'et' : 'Teema',
        'fi' : 'Aihe'
    },
    'MainPage' : {
        'en' : 'Main page',
        'et' : 'Pealeht',
        'fi' : 'Pääsivu'
    }//,
    //...etc
};

How to define a function for choosing a particular language:

function getText(lang, langKey) {
    //???????
    return langJson;
}

that outputs the same phrases like:

getText(lang, 'en'); //outputs {topic:'Topic',MainPage:'Main page',..}
getText(lang, 'et'); //outputs {topic:'Teema',MainPage:'Pealeht',..}
getText(lang, 'fi'); //outputs {topic:'Aihe',MainPage:'Pääsivu',..}

All the best: I

Answer 1

Basically you have to go through the whole lang object and pick the value for the correct language.

Object.keys will return an Array containing the keys of your initial lang object.
You can use those to create a new object.
You could use a for loop to iterate over those keys and add the corresponding value to the resulting object, but I like to use reduce to do so:

function getText(lang, langKey) {
  return Object.keys(lang).reduce(function(re, key) {
    re[key] = lang[key][langKey];
    return re;
  }, {})
}