Let's look at a template like this:

http://example.com/dictionary/{term:1}

We have two different behaviours depending upon the value used to expand term.

>>> import uritemplate
>>> u = uritemplate.URITemplate('http://example.com/dictionary/{term:1}')
>>> u.expand(term='foo')
'http://example.com/dictionary/f'
>>> u.expand(term=['foo', 'bar', 'bogus'])
'http://example.com/dictionary/foo,bar,bogus'

A simplified version of this is simply

{term:1}

In other words:

>>> import uritemplate
>>> u = uritemplate.URITemplate('{term:1}')
>>> u.expand(term='foo')
'f'
>>> u.expand(term=['foo', 'bar', 'bogus'])
'foo,bar,bogus'

All versions of uritemplate (and uritemplate.py) exhibit this behaviour and the RFC does not provide clear guidance.

I have not investigated how other implementations in other languages handle this, though. There do not appear to be any examples in the RFC that combine lists with length limitations.