Showing Tamil consonant sequences
Reference page: https://ta.wikipedia.org/s/4om
If you see in the above page, 'ஜ' follows 'ச'. Characters like 'ஸ', 'ஷ', 'ஜ', 'ஹ' etc. are called grantha characters which are not part of the basic alphabets of Tamil. See https://en.wikipedia.org/wiki/Tamil_script#Basic_consonants They are added towards the end (i.e. after 'ன') by convention. The first column in the attached image shows the correct sequence. (Image source: Naga. Ilangovan)
To fix this, we'll need to change the collation to uca-ta collation, and run the updateCollation.php script for all the Tamil wikis.