In MediaWiki 1.42.3, could you check: public_html/w/languages/i18n/en-gb.json ?
This is deployed with the language set to British English, but it seem to have some Yoruba terms in it (for example 'Talk' appears as 'Sọ̀rọ̀' and 'Change user groups' starts 'Ìyípo'). I have not been through every one.