saṃkrita subhāṣita - On things that cannot change

गुडपर्वतमध्ये  तु निम्बबीजं प्रतिष्ठितम्

क्षीरधारासहस्राणि निम्बः किं मधुरायते

Planted in the middle of a mountain of sugar,[watered by] thousands of of streams of milk, the seed of the neem [tree] cannot be sweetened. 

(lit. how can it be sweetened)

गुड - jaggery, sugar; masc. noun

पर्वत - mountain; masc. noun

मध्ये - in the middle; locative, singular of मध्य masc.noun

तु - but, and 

निम्बः - neem; masc. noun

बीजम् - seed; neuter noun

प्रतिष्ठितम् - placed, established, [here] planted past participle from prati+√sthā (1P)

क्षीरधारा - stream of milk

सहस्राणि - thousands

निम्बः - neem

किं - how

मधुरायते - to sweeten; denominative/नामधातु of madhura