Use appropriate foreign (particularly ancient Greek and Latin) plural forms where still in common usage
nucleus / nuclei stratum / strata genus / genera analysis / analyses basis / bases crisis / crises phenomenon / phenomena bacterium / bacteria millennium / millennia
Note that more than one plural form is sometimes in use for different meanings of a word.
formula / formulas in general—but formulae in maths/chemistry index / indices for maths—but indexes for books appendix / appendices for books—but appendixes in anatomy medium / media in general —but mediums for spiritualists datum / data in technical cases—but points of data in everyday use
European Commission English Style Guide - A handbook for authors and translators in the European Commission Eighth edition: January 2016. Last updated: July 2023 "[PDF File]" https://commission.europa.eu/system/files/2023-07/styleguide_english_dgt_en.pdf
University of Oxford Style Guide. "[PDF File]" Retrieved from https://www.ox.ac.uk/public-affairs/style-guide?wssl=