The `wb_terms_language` index on `wb_terms` is almost certainly not very useful (just ~400 distinct values over 600M+ rows), thus it can probably be dropped for good.
From db1087:
KEY `wb_terms_language` (`term_language`),
[x] dbstore2001.codfw.wmnet 3315
[x] db2089.codfw.wmnet 3315
[] db2086.codfw.wmnet 3315
[] db2085.codfw.wmnet 3315
[] db2084.codfw.wmnet 3315
[] db2083.codfw.wmnet 3306
[] db2082.codfw.wmnet 3306
[] db2081.codfw.wmnet 3306
[] db2080.codfw.wmnet 3306
[] db2079.codfw.wmnet 3306
[] db2075.codfw.wmnet 3306
[] db2038.codfw.wmnet 3306
[] db2045.codfw.wmnet 3306
[] db2052.codfw.wmnet 3306
[] db2059.codfw.wmnet 3306
[] db2066.codfw.wmnet 3306
[] db2023.codfw.wmnet 3306
[] labsdb1001.eqiad.wmnet 3306
[] labsdb1003.eqiad.wmnet 3306
[] labsdb1009.eqiad.wmnet 3306
[] labsdb1010.eqiad.wmnet 3306
[] labsdb1011.eqiad.wmnet 3306
[] db1095.eqiad.wmnet 3306
[] dbstore1001.eqiad.wmnet 3306
[] dbstore1002.eqiad.wmnet 3306
[] db1070.eqiad.wmnet 3306
[] db1071.eqiad.wmnet 3306
[] db1082.eqiad.wmnet 3306
[] db1087.eqiad.wmnet 3306
[] db1092.eqiad.wmnet 3306
[] db1096.eqiad.wmnet 3306
[] db1099.eqiad.wmnet 3306
[] db1100.eqiad.wmnet 3306
[] db1104.eqiad.wmnet 3306
[] db1106.eqiad.wmnet 3306
[] db1063.eqiad.wmnet 3306