|Very pretty, but no way to learn English.|
Worst of all, if they are dependent on a bilingual dictionary or translator, their knowledge of English exists in fragments. Each word they learn connects back to a word in their L1 (whether or not that word is an exact counterpart), rather than connecting to other English words and forming a network. English for them is a field of individual words, growing out of the bed of their L1.
What students need is for their L1 and L2 to be like two floors of a building. There may be several staircases going between the floors, but if you are on the L2 floor, and want to move to somewhere else on that floor, you don't go downstairs to L1, walk across that floor and up another staircase to L2 again. Instead, you walk across the L2 floor, following the network of connections that you have made between words in that language. Careful use of a monolingual dictionary, whether paper-based, online, or available as a smartphone app, can encourage this, as long as students learn to use all the information in the dictionary entry, not just the spelling and the basic definition.
In my experience, very few students take the time to work out for themselves the meanings of dictionary abbreviations such as U or C for nouns, or T or I for verbs, let alone figure out the phonetic transcriptions or study the usages in example sentences. So, most students will need dictionary training in class, comprising advice on how to choose and use a good dictionary, and 'dictionary drills' to rehearse and reinforce good dictionary skills. For lower level students, a student dictionary at their level will be useful for basic vocabulary. On the whole however, my belief is that dictionary use is best kept for self-study, and that classroom work should focus on developing the students' own vocabulary strategies and judgement.
Let's try extending the building metaphor to see how far it will go: the L2 floor has to be built from scratch. In the beginning there will be loads of scaffolding and ladders, with rickety planks between them. There will be areas of the floor that can't be reached, and the routes between the safe areas will be far from comfortable. Metaphor still working? I think so. There will need to be extra routes between the two floors - ladders, poles and ropes. Gradually you extend the scaffolding, and use it to put the floor down, removing the extra ropes and so on as you go.
And then you party.