This is an ongoing joke in the Pokemon series. Jessie and James memorized the motto incorrectly because they aren't the brightest, as explained by Cassidy and Butch in Episode 86.
The real motto as said by Cassidy and Butch:
Cassidy: Prepare for trouble
Butch: And make it double
Cassidy: To infect the world with devastation
Butch: To Blight all peoples in every nation
Cassidy: To denouce the goodness of truth and love
Butch: To extend our wrath to the stars above
Cassidy: Cassidy
Butch: Butch
Cassidy: Team rocket circling the earth both day and night
A YouTube video of this part is here:
https://www.youtube.com/watch?v=R5sgp2sn0Wg
In Japanese, the Team Rocket motto that Musashi and Kojirou (Jessie and James) recite goes like this:
ムサシ: なんだかんだと聞かれたら
コジロウ: 答えてあげるのが世の情け
ムサシ: 世界の破壊を防ぐため
コジロウ: 世界の平和を守るため
ムサシ: 愛と真実の悪をつらぬく
コジロウ: ラブリー・チャーミーな敵役
ムサシ: ムサシ
コジロウ: コジロウ
ムサシ: 銀河をかけるロケット団の二人には……
コジロウ: ホワイトホール、白い明日が待ってるぜ
ニャース: にゃんてにゃ
With a translation of (non-localized):
Musashi: If you ask us this or that...
Kojirō: The pity of the world is what responds!
Musashi: To prevent the destruction of the world!
Kojirō: To protect the peace of the world!
Musashi: To stand by the evils of love and truth!
Kojirō: The lovely, charmy villains!
Musashi: Musashi!
Kojirō: Kojirō!
Musashi: The pair from Team Rocket soars through the galaxy!
Kojirō: A white hole, a white tomorrow awaits us!
Nyarth: Something like that!
A YouTube video of Jesse and James performing their original motto can be found here:
https://www.youtube.com/watch?v=g7CNNYFhqdk
Interestingly enough, this joke doesn't seem to happen like it does in the English version. While they do claim to have the correct motto in Episode 86, their motto does not have the same tone the English version does.
Yamato and Kosaburou's (Cassidy and Butch) motto in the Japanese version is as follows:
ヤマト:何だかんだと聞かれたら
コサブロウ:答えないのが普通だが
二人:まあ特別に答えてやろう
ヤマト:地球の破壊を防ぐため
コサブロウ:地球の平和を守るため
ヤマト:愛と誠実な悪を貫く
コサブロウ:キュート でお茶目な敵役
ヤマト:ヤマト
コサブロウ:コサブロウ
ヤマト:宇宙を駆ける ロケット団の二人には
コサブロウ:ショッキングピンク桃色の明日が待ってるぜ
And the translation:
Yamato: If you ask us this or that...
Kosaburou: We usually don't respond
Both: But we'll make an exception this time and answer!
Yamato: To prevent the destruction of the Earth!
Kosaburou: To protect the peace of the Earth!
Yamato: To stand by evil with love and sincerity!
Kosaburou: The cute, mischievous villains!
Yamato: Yamato!
Kosaburou: Kosaburou!
Yamato: The pair from Team Rocket soars through the universe!
Kosaburou: Shocking pink, a pink tomorrow awaits us!
Additionally, I wasn't able to understand the joke about the "White Hole", so I've posted that as a question here: Why does Kojirou say "white hole" in the Japanese version of Team Rocket's motto?