Simple translate function requiring no external libraries. Includes plural form logic baked into closure. Feedback welcome

t.js

/**
 * Example Loco JavaScript export.
 * Usage: var singular = t('File');
 * Usage: var multiple = t('File','Files',3);
 * See: http://localize.biz/free/converter/api#to-js
 * Locale: pl_PL, Polish
 */
var t = function( pairs ){
    
    // named plural forms according to Unicode 
    var pluralForms = ["one","few","many"];
    
    // calc numeric index of a plural form (0-2)
    function pluralIndex( n ){
        return Number( (n==1 ? 0 : n%10>=2 && n%10<=4 && (n%100<10 || n%100>=20) ? 1 : 2) );
    }

    // expose public t() function
    return function( msgid1, msgid2, n ){
        var value  = pairs[msgid1];
        if( arguments.length < 2 ){
            if( null == value ){
                return msgid1||'';
            }
            if( 'string' !== typeof value ){
                value = value.one;
            }
            return value;
        }
        // plural operation
        n = pluralIndex( n );
        value = value ? value[ pluralForms[n]||'other' ] : null;
        if( null == value ){
            return n ? msgid2||msgid1 : msgid1;
        }
        return value;
    }
}(
    {"File":{"one":"Plik","few":"Pliki","many":"Pliko'w"}}
);

Working on neat design pattern for a machine-generated script for the Loco language pack converter

The translations and plural rules are baked into the closure to avoid external dependencies.