Isaiah 33:19

There shalt thou not see a people of a strange tongue to have so diffused a language, that it may not be understood: neither so strange a speech but it shall be perceived.

Isaiah 28:11

And therefore the LORD also shall speak with lisping lips and with a strange language unto this people, to whom he spake afore of this manner:

Deuteronomy 28:49-50

"And the LORD shall bring a nation upon thee from afar, even from the end of the world, as swift as an eagle flyeth: a nation whose tongue thou shalt not understand;

Jeremiah 5:15

Lo, I will bring a people upon you from far, O house of Israel, sayeth the LORD; a mighty people, an old people, a people whose speech thou knowest not, neither understandest what they say.

2 Kings 19:32

Wherefore thus sayeth the LORD, of the king of Assyria: He shall not come to this city, nor shoot arrow into it, nor come before with shield nor cast any bank against it -

Ezekiel 3:5-6

For I send thee not to a people that hath a strange, unknown, or hard speech, but unto the house of Israel;

Exodus 14:13

And Moses said unto the people, "Fear ye not, but stand still and behold how the LORD shall save you this day: For as ye see the Egyptians this day, shall ye see them no more forever till the world's end.

1 Corinthians 14:21

In the law it is written, "With other tongues, and with other lips will I speak unto this people, and yet for all that will they not hear me, saith the Lord."

Treasury of Scripture Knowledge

Summary

Thou shalt not see a fierce people, a people of a deeper speech than thou canst perceive; of a stammering tongue, that thou canst not understand.

Bible References

Shalt not

Exodus 14:13
And Moses said unto the people, "Fear ye not, but stand still and behold how the LORD shall save you this day: For as ye see the Egyptians this day, shall ye see them no more forever till the world's end.
Deuteronomy 28:49
"And the LORD shall bring a nation upon thee from afar, even from the end of the world, as swift as an eagle flyeth: a nation whose tongue thou shalt not understand;
2 Kings 19:32
Wherefore thus sayeth the LORD, of the king of Assyria: He shall not come to this city, nor shoot arrow into it, nor come before with shield nor cast any bank against it -

Deeper

Isaiah 28:11
And therefore the LORD also shall speak with lisping lips and with a strange language unto this people, to whom he spake afore of this manner:
Jeremiah 5:15
Lo, I will bring a people upon you from far, O house of Israel, sayeth the LORD; a mighty people, an old people, a people whose speech thou knowest not, neither understandest what they say.
Ezekiel 3:5
For I send thee not to a people that hath a strange, unknown, or hard speech, but unto the house of Israel;
1 Corinthians 14:21
In the law it is written, "With other tongues, and with other lips will I speak unto this people, and yet for all that will they not hear me, saith the Lord."