VisualEditor has some techniques for this (e.g. to make sure it's editable as JSON).
The simple version of this is to just allow:
More elaborate variations could support dates as well (e.g. August 2015). But I think just consecutive numbering is probably fine.
We should also investigate whether we can have this translated at MediaWiki.org while still allowing wiki-specific overrides by editing the MediaWiki.org page.
See T117616: Allow config of archive page title formats for LQT conversion using MediaWiki namespace config page.