Here the Windows-log excerpt (the 5 cyrillic letters stay uppercased):
LOG: database system is ready to accept connections
LOG: autovacuum launcher started
LOG: statement: SET client_encoding = 'UTF8';
LOG: execute <unnamed>: SELECT out_gid AS gid FROM words_play_game($1, $2, $3::jsonb)
DETAIL: parameters: $1 = '1', $2 = '3', $3 = '[{"col":7,"letter":"П","row":11,"value":2},{"col":7,"letter":"И","row":10,"value":1},{"col":7,"letter":"Л","row":9,"value":2},{"col":7,"letter":"О","row":8,"value":1},{"col":7,"letter":"П","row":7,"value":2}]'
NOTICE: tile = {"col": 7, "row": 11, "value": 2, "letter": "П"}
NOTICE: letter = П
NOTICE: tile = {"col": 7, "row": 10, "value": 1, "letter": "И"}
NOTICE: letter = И
NOTICE: tile = {"col": 7, "row": 9, "value": 2, "letter": "Л"}
NOTICE: letter = Л
NOTICE: tile = {"col": 7, "row": 8, "value": 1, "letter": "О"}
NOTICE: letter = О
NOTICE: tile = {"col": 7, "row": 7, "value": 2, "letter": "П"}
NOTICE: letter = П
