Various translations disagree over whether Zephaniah 3:9's עַמִּ֖ים (amm-im) should be 'people' or 'peoples'. A multitude of nations are mentioned throughout Zephaniah, but apart from this single verse I can't see any evidence for these nations receiving any kind of salvific concern. In essence, this word and verse alone seems to make or break the case for whether Zephaniah's prophecies solely cover the salvation of Judah or have a wider application to the nations.
New International Version
"Then I will purify the lips of the peoples, that all of them may call on the name of the LORD and serve him shoulder to shoulder.
English Standard Version
“For at that time I will change the speech of the peoples to a pure speech, that all of them may call upon the name of the LORD and serve him with one accord.
King James Version
For then will I turn to the people a pure language, that they may all call upon the name of the LORD, to serve him with one consent.
Even the JPS seems to go with 'peoples' in the plural, so this doesn't appear to be a Christianisation of the text, either:
For then will I turn to the peoples A pure language, That they may all call upon the name of the LORD, To serve Him with one consent.
The NET does something strange and does a full-on change to the word 'nations', probably carrying through the subject of the previous verse:
New English Translation
Know for sure that I will then enable the nations to give me acceptable praise. All of them will invoke the LORD's name when they pray, and will worship him in unison.
What's the best translation of this verse? Are there any textual variants in play here, or are the various translations purely coming out of an ambiguity in the plural at the end of עַמִּ֖ים?