וַיִּצָּעֵק֙ אִ֣ישׁ אֶפְרַ֔יִם וַֽיַּעֲבֹ֖ר צָפ֑וֹנָה וַיֹּאמְר֨וּ לְיִפְתָּ֜ח מַדּ֣וּעַ ׀ עָבַ֣רְתָּ ׀ לְהִלָּחֵ֣ם בִּבְנֵי־עַמּ֗וֹן וְלָ֙נוּ֙ לֹ֤א קָרָ֙אתָ֙ לָלֶ֣כֶת עִמָּ֔ךְ בֵּיתְךָ֕ נִשְׂרֹ֥ף עָלֶ֖יךָ בָּאֵֽשׁ׃
Ephraim’s contingent mustered and crossed [the Jordan] to Zaphon. They said to Jephthah, “Why did you march to fight the Ammonites without calling us to go with you? We’ll burn your house down over you!”
The above rendering comes from the RJPS translation—an adaptation of the NJPS translation—showing a slight modification projected for October 2023. Before accounting for this rendering, I will analyze the plain sense of the Hebrew term containing אִישׁ.)
On the “collective” usage of the singular אִישׁ in the context of hostilities, see my comment at 7:23. On its profiling this referent as a contingent of the Israelite forces under Jephthah’s command, see my comment at 7:24. Here, as in 8:1, there is also an aspect of a parley between two parties; on such usages, see my comment at Josh 9:6.
As for rendering into English, see my comments at Josh 7:24, at 10:24, and at Judg 8:1.