Is someone's spoken language judged by tone or articulation of words?

Both! using one without the other can quite easily cause misunderstandings.

If it's the speaker's first language, there should be a certain degree of mastery over L1 and this includes all the dimensions of the language. If it's L2, it depends on the amount and type of input-output practice that the speaker has been involved in.Thus, the level of proficiency determines how to assess the speaker's language competence or speaking fluency.

I think as long as this person isn't a teacher ,the only and best measure is understanding.

by both of them , all the factors of speaking should be existed