Mongoose.js schema description issue (array vs object)

I need to store some user dictionaries (sets of words, and I need to store it as user property) and each dictionary has actually only one property: language.

So I can describe that property like that:

dictionaries:[{language: 'string', words: [.. word entry schema desc..]
    }]

and store dictionaries like that:

dictionaries: [
   {language: en, words: [.. words of English dictionary..]},
   {language: es, words: [.. words of Spanish dictionary..]}
]

But actually I could store the dictionaries in "less nested" way: not array abut object:

dictionaries: {
   en: [.. words of English dictionary..],
   es: [.. words of Spanish dictionary..]
}

But I don't see a way to describe such object with mongoose schema. So the question is what is the best (more reasonable in terms of storage and querying) option to go with considering I use mongoose.