The verse appears in the Masoretic Text and LXX as follows, respectively -
Psalm 19:3 (MT)
3 אֵֽין־אֹמֶר וְאֵין דְּבָרִים בְּלִי נִשְׁמָע קֹולָֽם׃
The literal translation - There is no speech and there are no words: their voice is not heard.
Psalm 19:1-3 (LXX)
3 οὐκ εἰσὶν λαλιαὶ οὐδὲ λόγοι ὧν οὐχὶ ἀκούονται αἱ φωναὶ αὐτῶν
The literal translation - There are no speeches and there are no words, of which their voices are not being heard.
Please click here to view the expanded analysis of this verse in both Greek and Hebrew.
What we see here is the double negative, which appears in Isaiah, when the Lord describes Himself as "the First and Last" (Is 44:6) after indicating that there are no gods before Him nor are there any gods after Him (Is 43:10-11). In other words, the Almighty Lord is transcendent, and this transcendence is understood through terms in the double negative. Otherwise, the simple positive propositional statement "God is eternal" would in no way convey this nuance of transcendence; the double negative however does convey the nuance that nothing is transcendent before (beyond) His non-beginning, and nothing exists after (beyond) His non-ending. This double negative also occurs here in the Psalms, but now with the glory of God in view.
The first two verses in this Psalm indicate the universality of the "spoken" declarations of glory of God. In the vertical sense, the heavens declare this glory, and in the horizontal sense, the earth ("from day to day and night to night") declares this glory. The double negative now is to say that there is NO such place (heaven or earth) or time (day or night) where this glory is NOT declared. An expanded colloquial translation of the third verse therefore would be as follows -
Psalm 19:1-3
1 The heavens are telling of the glory of God;
And their expanse is declaring the work of His hands.
2 Day to day pours forth speech,
And night to night reveals knowledge.
3 There are no speech or words extant (in God's creation),
Where this voice (of God's glory) is not heard.