All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Tajweed (set of rules governing the way in which the words of the Quran should be pronounced) is of two types: one is desirable to learn, which is the one related to articulating the Madd (extended vowels), Ghunnah (a sound that comes out from the nasopharynx), and other matters that do not affect the correct recitation. The second is a Waajib (obligatory), which is the one related to pronouncing the letters from the correct spot of articulation.
Therefore, you must look for a trustworthy Shaykh who masters the science of Tajweed in your town or elsewhere, so that you will correct your recitation, particularly Al-Faatihah, because one's prayer is not valid without this (proper pronunciation of Al-Faatihah).
We do not think that this is impossible; if you recite Al-Faatihah (in particular) with the correct recitation, then your prayer will be valid, and you will not be sinful for delaying the learning of the recommended Tajweed until you are able to do so, but it is better to hasten and learn.
Thereafter, if you still fail to utter some letters properly because the language is foreign to you despite you exerting all efforts, then you are excused and your prayer in this situation is ruled to be valid.
Some scholars are lenient about the pronunciation of some letters that have converging articulation spots, and which are difficult for the common Muslims to distinguish between them, such as ض and ظ , and some scholars considered ط and ت to be the same case, as well as س and ص; so they do not consider the prayer of one who fails to pronounce them properly to be invalid.
To sum up, it is not difficult for you to look for a Shaykh who masters the proper pronunciation of the Quran to teach you how to correctly pronounce Al-Faatihah. Therefore, you should hasten in finding one to make sure your prayer is valid.
Allah knows best.