He also will become a people, and he also will be great
Here "He" refers to Manasseh, but it stands for his descendants. AT: "Your older son will have many descendants, and they will become a great people" (See: rc://en/ta/man/translate/figs-metonymy)
that day with these words
"that day, saying"
The people of Israel will pronounce blessings by your names saying
"The people of Israel will speak your names when they are blessing others"
by your names saying, 'May God make you like Ephraim and like Manasseh'
This is a quotation within a quotation. It can be stated as an indirect quotation. AT: "by your names. They will ask God to make others like Ephraim and like Manasseh" (See: rc://en/ta/man/translate/figs-quotesinquotes and rc://en/ta/man/translate/figs-quotations)
like Ephraim and like Manasseh
Israel saying Ephraim's name first is another way he indicates that Ephraim will be greater than Manasseh.
Israel put Ephraim before Manasseh
Giving Ephraim the greater blessing and making him more important than Manasseh is spoken of as if Israel physically put Ephraim in front of Manasseh. (See: rc://en/ta/man/translate/figs-metaphor)