use fulltext formsof inflectional to generate terms
You can find the words that will be used in the match with the sys.dm_fts_parser function in SQL Server.

The Syntax

sys.dm_fts_parser('query_string', lcid, stoplist_id, accent_sensitivity)


I won't go in details for the parameters values, but the "lcid" is important.  In the example below I'm using 1033 which is for English - US.  I've tried with 1036, French - Standard, and for sure I didn't get any results beside the word itself, since the word doesn't exist in the French dictionary.

Example

SELECT display_term
FROM SYS.DM_FTS_PARSER('FORMSOF(INFLECTIONAL, welcome)', 1033, 0, 0)


Result

welcome's
welcomed
welcomes
welcomes'
welcoming
welcome