No Paul didn't speak English and he uses a different than Jesus did. The two different words are both translated to English is some translations as world.
kosmos in Rom. 1:8 - planet earth as a place of inhabitation, the world
oikoumene in Matt 24:14 - the earth as inhabited area, exclusive of the heavens above and nether regions, the inhabited earth, the world
In the BDAG, the actual definition is given in italics.
Your argument falls apart apart from this because of Col. 1:23 -
If ye continue in the faith grounded and settled, and be not moved away from the hope of the gospel, which ye have heard, and which was preached to every creature which is under heaven; whereof I Paul am made a minister; (Col 1:23, KJV)
More than likely, "world" in Matt. 24:14 was referring to the Roman Empire and the same with Rom. 1:8. So, Romans 1:8 surely still fulfills the prophecy of Matt. 24:14. The verse in Colossians is quite emphatic.