Handling deep conditional logic [on hold]

How about this approach:
MY_RESOURCES is a global variable here, which allows you to access the strings. (I hope such a thing already exists for your project?)

string getWord(wordname, language){
    return MY_RESOURCES.get(wordname, language)
}

string adult(num_adults) {
    return (num_adults > 1) ? getWord("adult", CURRENT_LANGUAGE) : getWord("adults", CURRENT_LANGUAGE);
}

string child(num_children) {
    return (num_children > 1) ? getWord("child", CURRENT_LANGUAGE) : getWord("children", CURRENT_LANGUAGE);
}

string generateText(num_children, num_adults) {
    string result = "";
    if (num_children > 0){
        result += String.valueOf(num_children) + " ";
        result += child(num_children);
    }
    if (num_children > 0 && num_adults > 0){
        result += getWord("and", CURRENT_LANGUAGE);
    }
    if (num_adults > 0) {
        result += String.valueOf(num_adults) + " "
        result += adult(num_adults);
    }
    return result;
}