Best practice is to have a language tag on all text literals that are language dependent. Some text literals are not language dependent (identifiers). These should be marked as xsd:string
By adding language tags, we position the ontology files for internationalization. Additional text values can be added for other languages with appropriate language tags. Software can then choose the appropriate language to display, given local context.
This issue is also https://github.com/openrif/vivo-isf-ontology/issues/700