Kaddish: Hebrew or Aramaic?
Although most of our prayers are in Hebrew, there are a number of prayers that are in Aramaic. The most prominent of these Aramaic prayers is certainly the kaddish. Although the kaddish is indeed recited in Aramaic, this might not have always been the case. This is because in one place the Talmud cites the kaddish in Aramaic  while in other places it cites it in Hebrew.
How do we resolve this discrepancy?
It is quite likely that the kaddish was first composed and recited in Hebrew. It was only much later that the switch to Aramaic was made. As Tosfot explains: “The kaddish was originally recited in Hebrew. However, since not everyone understood Hebrew in those days, the kaddish began to be recited in Aramaic. This change was made in an effort to ensure that the masses would be able to better understand the meaning of this important prayer, as Aramaic was the primary spoken language of the time.” The Tur writes similarly.
There is another theory as to why Kaddish is recited in Aramaic. Kaddish was originally intended to be recited in Hebrew. At some point in history, however, the secular authorities decreed that it was forbidden for Jews to praise God. Therefore, in order to ensure that the authorities would not understand what they were saying, the Kaddish began to be recited in Aramaic. Even when the decree was lifted, it was decided to retain the Aramaic recitation of kaddish in order to recall the decree that had once been made.
Rav Chaim David Halevy was asked if it is permissible to revert back to the original practice of reciting kaddish in Hebrew, as Aramaic is no longer spoken nor is it even widely understood. In a somewhat surprising ruling he writes that doing so is essentially permissible. Nevertheless, he cites the Zohar which insists that kaddish must only be recited in Aramaic. He therefore concludes that no change should be made in deference to the view of the Zohar. We see from here that it is especially important that one understand the kaddish, and therefore, one should make an effort to learn the meaning of the words. The Siddur "Rinat Yisrael" has translated all the Aramaic prayers into Hebrew, including kaddish, for this reason. Truth be told, the kaddish contains both Hebrew and Aramaic components that are woven together to praise God in a very specific and exalted fashion.
On a related note, it is preferable to pray in Hebrew, even if one does not understand the meaning of the words, rather than to pray in a language that one understands. Indeed, one should even pray from an English transliterated text in order to be able to recite them in Hebrew. This is because the Hebrew language is inherently holy and this holiness ensures that one's prayers are effective even if one doesn’t fully understand them. In contrast, one is required to understand the meaning of the words one recites when praying in a language other than Hebrew in order for one's prayers to be effective.
It is also taught that the angels assist us in having our prayers being favorably received before God. However, this "angelic advantage" is not present when prayers are recited in Aramaic. This is because Aramaic is a language that most angels don’t understand. As such, it might be preferable to recite Aramaic prayers, such as Brich Shmei and Yekum Purkan, in Hebrew or English if one does not understand the meaning of the words. This is especially true when praying alone, as one does not enjoy the same spiritual benefits when one prays alone that praying with a minyan has to offer. In fact, many authorities rule that the Aramaic components of the selichot prayers should be omitted when one prays alone.
On the other hand, there is a view that Aramaic is so closely related to Hebrew that it actually assumes the same status as Hebrew. Indeed, the Midrash warns us not to treat the Aramaic language lightly since the Torah itself uses it. According to this approach, praying in Aramaic offers the same advantages as praying in Hebrew and one's prayers are effective even if one doesn’t understand the meaning of the words.
 Sota 49a.
 Berachot 3a, 21b.
 Berachot 3a.
 Tur, OC 56.
 Tanya Rabati s.v. “hazemirot.”
 Aseh Lecha Rav 3:12.
 Pardes Hagadol 5.
 OC 101:4; Biur Halacha 101; Aruch Hashulchan, OC 101:9, 185:4; Mishna Berura 193:5; Kaf Hachaim, OC 101:16. But see Magen Avraham 101:5; Sefer Chassidim 588 and 785 for a dissenting view.
 Bemareh Habazak 2:1.
 Elya Rabba, OC 56:5; Tosfot, Shabbat 12b.
 OC 101:4; Mishna Berura 101:19; Mateh Ephraim 581:21.
 Maharsha, Shabbat 77b; Shu"t Harama 126.
 Bereishit Rabba 74:14.