DLC files for commentary (Language Packs) must be installed separately if you want audio in languages other than English.
Ensure your like Atmosphere or SX OS is updated to support the latest firmware requirements. Install the base game (.XCI or .NSP) first. FIFA 21 Legacy Edition Switch XCI/NSP Update ...
Install the file using your preferred installer (Tinfoil, Goldleaf, or DBI). DLC files for commentary (Language Packs) must be
Latest transfers and squad depth adjustments. FIFA 21 Legacy Edition Switch XCI/NSP Update ...