What are the three major approaches of machine translation ?

Direct MTApproach 
The Direct Translation approach works by translating the source language directly into the target language, without any intermediate representation. This method often operates at the word or phrase level, using dictionaries and rules to handle lexical, morphological, and syntactic differences between languages. While this approach can result in speedy translations, it can also lead to inaccuracies and difficulties in coping with complex language structures.

Transfer Approach
The Transfer-Based Translation approach involves converting the source language into an intermediate representation that captures its syntactic and semantic structure. This intermediate representation is then used to generate a translation in the target language, subsequently processed through linguistic rules and transformations. Although typically more computationally expensive than direct translation, transfer-based translation can produce higher-quality translations by preserving the structure and meaning of the source text.

Interlingua approach
Lastly, the Interlingua-Based Translation approach translates the source language into an abstract, language-independent representation called "interlingua." The target language translation is then generated from the interlingua. This approach is advantageous for multilingual translation scenarios, as only two translation steps are needed between any pair of languages. However, creating a comprehensive interlingua that can express different language structures accurately is a challenging task.