As a first-year masters student in a non-English speaking country who is considering to later continue to study Ph.D. abroad (US or Canada), which option would be more desirable? Publishing in a medium quality (locally held) international conference which is in English (and indexed by IEEE Xplore) or a higher quality (local) non-English conference or journal?
Clarification: neither conference is top by international standards. It's a question of comparing two nationally known conferences where the English one has less national reputation.
Which conference to publish in depends on your goals for the publication:
Conferences can be extremely valuable networking opportunities, and speaking at a conference puts your work in front of the audience of that conference. If the non-English venue is a community that will be valuable for you to connect with, then publishing there can be extremely helpful with building professional contacts, getting into a good Ph.D. program or getting a good job, etc. Note that this may apply even if you're planning to study abroad later, as those colleagues may have overseas contacts.
On the other hand, sometimes you are less interested in the interactions at the conference than in just having a "this is published" stamp and collecting citations for another line in your C.V. In this case, it's not the conference itself but the online accessibility of the paper that's likely to be matter more to you, and it will likely to be more valuable to have it in English if your subfield is (like most currently are) English-dominated.
Note also that you may be able to gain the benefits of both by a follow-on journal publication. If you are in a field where it is typical for conference publications to be upgraded into a more archival "extended form" journal publication (e.g., computer science), then you might publish originally in the other language, then follow up with an English journal publication, thus obtaining both sets of benefits, though at a cost of having the English version come out much later.