Some important factors that contribute to learning foreign languages are:
1. The learner's motivation and language ability or skills: In language learning it is true that the learner's motivation and determination is crucial. Where there is a will, there is a way. Highly motivated learners make use of every opportunity to attain their learning goals, no matter how complicated the language is.
Language ability varies from person to person, but learning foreign languages is always better and easier before puberty. After that period, it is more and more difficult. It is true that after the age of 18, most language learners usually have a foreign accent.
2. Time devoted to learning the target language: The longer, the better, of course. Therefore, foreign languages should be taught to young children (at kindergarten, or even earlier). Practice regularly, every day and everywhere possible.
3. Context of language acquisition: Immersion in the culture or living in the country where the target language is spoken is the best way to learn and master that language. Languages are living. Therefore, they need to be learned in natural contexts in life. Watching films, listening to and singing songs, getting engaged in role plays or games.... That is, direct (or indirect) interactions with native speakers is the best and the most interesting way to learn the language.
4. Learners' attitudes and characters: Learners should be bold and adventurous. Shyness is a huge hurdle that the learner needs to get over in learning a foreign language. Learners must be actively engaged in the learning process, without any fear of making mistakes. In addition to speaking and listening, reading, writing (poetry, diary, essays, articles, blogs....), and composing (lyrics or words for songs/music) will certainly help the leaner hone and master all the necessary skills in the target language.
Flash cards to develop vocabulary, translation (or interpretation), sentence structure/grammar drills and memorization (rote memory) of passages written in the target language... may work well for some learners, but such methods are passive, and dependent on short-term memory. Actually, translation is not a simple and easy way to learn foreign languages, and should be regarded as an art suitable to those who have mastered the fundamentals in both languages, and would like to hone their skills in language expression at higher levels. Unless the translation version is double checked by some experts (in the subject matter), the product is often subjective. In addition, a good translator is expected to know the two cultures well enough to be able to find equivalent expressions in natural and fluent ways.
Finally, learners need to know that languages are living and evolving. Thus, language learning never comes to an end, and should be considered as living that target language till the end of the learner's life.