The Moabite Stone has proved this conclusively.

Moabite and Ammonite, Phoenician and Hebrew, were all alike dialects of one language, which differed from one another merely as one English dialect differs from another.

Hebrew had retained a few "Arabisms," a few traces of its ancient contact with Arabic-speaking tribes; that was all.

In other respects it was the same as "the language of Canaan" on either side of the Jordan.
The Ammonites believed themselves to be the children of the national god Ammi.

But Ammi was usually worshipped under the title of Malcham or Milcom, "the King." It was to Milcom that Solomon erected an altar at Jerusalem, in honour of that Ammonite wife whose son Rehoboam succeeded him on the throne, and it was from the head of his image at Kabbah that his crown of gold and precious stones, 131 pounds in weight, was removed to grace the triumph of David.[8] Moab was more exposed to the inroads of its nomadic neighbours from the wilderness than its sister-kingdom of Ammon.