In plain words
Or else one is born into a family of wise yogins. Such a birth is indeed far more difficult to obtain in this world.
Word for word
Or else [he] is born in the family of wise yogins indeed; for this birth, which is such, is harder to obtain in the world.
अथवा योगिनामेव कुले भवति धीमताम्एतद्धि दुर्लभतरं लोके जन्म यदीदृशम्
Other commentaries
The commentators
▸Bhagavadgītābhāṣyam· bhāṣya
अथवा श्रीमतां कुलात् अन्यस्मिन् योगिनामेव दरिद्राणां कुले भवति जायते धीमतां बुद्धिमताम् । एतत् हि जन्म, यत् दरिद्राणां योगिनां कुले, दुर्लभतरं दुःखलभ्यतरं पूर्वमपेक्ष्य लोके जन्म यत् ईदृशं यथोक्तविशेषणे कुले ॥ ४२ ॥
In plain words
Or else he is born somewhere other than a wealthy house: into a family of yogins who own nothing. And dhīmatām — the wise, the clear-minded ones. This birth, in the family of poor yogins, is the harder one to come by; set beside the first, it costs more to win. A birth of just this kind, in a family marked by everything named here.
Close to the Sanskrit
Or else — other than from a family of the wealthy, in another, that is, in a family of yogins who are poor — he comes to be, is born; dhīmatām means buddhimatām, of the intelligent. For this birth, which is in a family of poor yogins, is durlabhataram, that is, harder to obtain, in reference to the former, in the world — a birth which is īdṛśam, of such a kind, in a family having the qualifications as stated.