(Disclaimer: There is no caste system in Gita and Varna was not birth based originally)
Let us first see the shloka:
श्रेयान्स्वधर्मो विगुणः परधर्मात्स्वनुष्ठितात्।
स्वभावनियतं कर्म कुर्वन्नाप्नोति किल्बिषम्।।18.47।।
observation1: It does not even mention 'Varna" as word. It mentions "swadharma" and "par-dharma"
See various translations of it at Gita Supersite
English Translation By Swami Adidevananda
18.47 Better is one's own duty, though ill done, than the duty of another, though well-performed৷৷৷৷৷৷ When one does the duty ordained by his own nature, he incurs no stain.
English Translation by Swami Gambhirananda
18.47 One's own duty, (though) defective, is superior to another's duty well performed. By performing a duty as dictated by one's own
nature, one does not incur sin.
English Translation by Swami Sivananda
18.47 Better is one's own duty (though) destitute of merits, than the duty of another well performed. He who does the duty ordained by his
own nature incurs no sin.
English Translation Of Sri Shankaracharya's Sanskrit Commentary by Swami Gambhirananda
18.47 Svadharmah, one's own duty; though vigunah, defective-the word though has to be supplied-; is sreyan, superior to, more praiseworthy than; paradharmat, another's duty; su-anusthitat, well performed. Kurvan, by performing; karma, a duty; svabhavaniyatam, as dictated by one's own nature-this phrase means the same as svabhavajam (born from Nature) which has been stated earlier-; na apnoti, one does not incur; kilbisam, sin. As poison is not harmful to a worm born it it, so one does not incur sin by performing a duty dictated by one's own nature. It has been siad that, as in the case of a worm born in poison, a person does not incur sin while performing his duties which have been dictated by his own nature; and that someone else's duty is fraught with fear; also that, one who does not have the knoweldge of the Self, (he) surely cannot remain even for a moment without doing work (cf. 3.5).
English Translation of Ramanujacharya's Sanskrit Commentary by Swami Adidevananda
18.47 One's proper Dharma is that which is suitable for performance by oneself, in the form of worshipping Myself, relinishing agency etc., as has been taught. For, Karma Yoga, consisting in the activities of sense organs, is easy to perform by one in association with Prakrti. Thus, Karma Yoga, even if it is defective in some respects, is better than the Dharma of another, i.e., than Jnana-yoga, even for a person capable of controlling his senses, which is an attainment liable to negligence, because it consists of control over all sense-organs; for, though this may be well performed occasionaly, one is always liable to deflection from it. He explains the same: As Karma consists of the activities of the sense-organs, it is ordained by Nature for one who is conjoined with Prakrti, i.e., the body. So by performing Karma Yoga one does not incur any stain. But Jnana Yoga is liable to negligence, because it reires the control of the senses from the very beginning for its performance. One intent on it is likely to incur stain from negligence. [Thus we are reminded about what was mentioned in the third chapter - that Karma Yoga alone is greater.]
English Translation By By Dr. S. Sankaranarayan
18.47. Better is one's own prescribed duties, [born of one's nature, even though] it is devoid of ability, than another's duty well executed;
the doer of duty, dependent on (or prescribed according to) one's own
nature, does not incur sin.
English Translation by Shri Purohit Swami
18.47 It is better to do one's own duty, however defective it may be, than to follow the duty of another, however well one may perform it He who does his duty as his own nature reveals it, never sins.
You may get Hindi translation from the same url too.
CONCLUSION : None of the English/Hindi translation "from so many acharyas" of different panthas/different sects, yet none of them has mentioned "varna"/caste" in this shloka. All of them mention about "Swadharma"(own duties). Now a non-alert translator can see caste/varna/discrimination embedded in the verses, where there is not even an inkling of it.