The correct option is B those of other countries
The nouns being compared in the given sentence are the languages of India with the languages of other countries in terms of number. The underlined phrase mentions only 'other countries' and misses out on their languages, hence option D is incorrect. In option B, we're shown the phrase 'those of other countries'. 'Those' demonstrates the phrase 'the languages' hence this is the correct option. In options A and C the phrases are incomplete. In A 'languages' is not mentioned, whereas in C 'countries' is not mentioned, so these two are incorrect.