כִּ֚י בְּלַעֲגֵ֣י שָׂפָ֔ה וּבְלָשׁ֖וֹן אַחֶ֑רֶת יְדַבֵּ֖ר אֶל־הָעָ֥ם הַזֶּֽה׃
װאָרום מיט אַ שטאַמלדיקער ליפּ, און מיט אַ פֿרעמדן לשון, מוז מען רעדן צו דעם דאָזיקן פֿאָלק,
Rashi
With distorted speech (בְּלַעֲגֵי שָׂפָה) Similarly, לְעָגִים and (infra 32:4), עִלְּגִים, are both expressions of distorted speech, which is not readily grasped.
Ibn Ezra
בלעני שפה With laughing12A. V., Stammering. lips. Comp. לענ derision (Ps. lxxix., 4). The teacher speaks to the child in a laughing and mocking way.
Rashi
he speaks to this people Everyone who speaks to them words of prophecy or admonition is to them like a distorted language, which they cannot understand.