I am personally working on this aspects in the language teaching and learning process (through my own empirical observation too). It seems to me that the traditional methods are not including a multilingual neither a bilingual receptor/learner/classroom. Besides, every bi- or multilingual learner presents different tools and techniques towards the language learning process due to their own personal level of command in the other languages.
For example, if we consider a bilingual country with a wider number of speakers compared to adult language course where language command varies according to their own personal experience, or else in an international school where the resources, amount of student with multilingual skills is more frequent (although they all manage differnte language and cultural context).
In order to answer to your question, I suggest to look further in the techniques multilingual students (different from bilingual students do) apply when learning a new language. Their world view and the way they approach to a learning experience is definitely more holistic as they use listening skills (conected to memories) to related associate similar but different words, opposite words, cognates and false cognates to make quick understandings of the meaning of words, phrases and idiomatic expressions; also visual realia (maps, bills, event leaflets, videos and multimedia resouces), needless to say that kinesthetic sources (smells, flavours, family memories, trips, you name it).
The audio-visual material is not all but motivates a lot more to activate the memory experience of the language rather a more traditional method.
I would recommend an integral program of many methods rather than only one, audio lingual, direct method, with a twist a functional everyday pieces of language and real situation dialogues plus cultural knowledge of the target language (fun facts, touristic tips, history, commemoratiin and holidays facts). Plus a more oral presentation-like (out-put) style of evaluation rather than a paper/grammar-base/mechanic quiz or tests.
Hello. I teach linguistics and language pedagogy papers in Education department. I think your overall approach rather than 'method' is more important here. And your approach goes back to the framework you locate the nature of language and language teaching in. If you perceive language mainly in terms of grammar and structure, you tend to take up structural approaches (with a focus on grammatically well-formed sentences) more than communicative. On the other hand, if you perceive language as a medium of thought and communication, mainly a Functional approach (ref. Halliday's 'Functions of language), you tend to take a more Communicative (and Holistic) approach. Methods are decided accordingly. The best methods are based on a holistic approach where holistic is in terms of linguistic levels (lexical, syntactic and so on) as well as in terms of the domains of language skills, mainly but not limited to LSRW. Hope this helps !
This is an importsnt question because most learning environments are bilingual, but operated through monolingual teaching methods. A mixed method approach is suitable for different ahe groups and skill levels.