There are some things in music where there are standards and standard usages. Much of standard notation is, well, standard; things like the MIDI protocol and file formats are standardised; a concert pitch of A4=440 is an agreed-on standard (albeit not the only one).
However, when it comes to what notes and tonalities to choose, There is (thankfully!) no agreed-upon "standard usage" in music. The original phrasing - that Locrian is rarely used - is more precise.
The other sense in which 'standard' could be used is to indicate that a concept is commonly understood - whether the word has a 'standard' meaning. In this sense, modern 'Locrian' probably is standard, because what the word 'Locrian' means is recognised and understood alongside the other mode names.