Orthography can vary significantly from one language to another. Though the Roman alphabet is widely used and many sounds are represented by the same letter in various languages, many differences also exist. I will give examples.
The vowel sound of moon is u in many languages. In Spanish the word for moon is luna. However, this vowel sound is written oe in Dutch. The Dutch word for group is groep.
The initial consonant sound of cheese is ch in English. In Hungarian, though, this sound is spelled cs. The Hungarian word for bone is csont.
The letter s is spelled sz in Hungarian. The Hungarian word for sandwich is szendvics. In Hungarian, the letter s corresponds to the English sh.
In French the letter s is pronounced as a z in intervocalic position. For example, the s in the word poison (same meaning and spelling as in English) is pronounced as a z because it comes between vowels.
The vowel sound of toy is spelled eu in German. The German word for friend is Freund. In Portuguese this sound is represented by oi as in oito (eight).
The j of English as in juice is pronounced differently in other languages. In Portuguese the j has the sound of the s in treasure as in janela (window). In Spanish the j is similar to the h of English. The Spanish word hijo (son) has a silent h and a j that sounds similar to the h of house. In German the j is pronounced as a y in English. For example, the word ja (yes) is pronounced with the initial sound of yellow.
It is clear that the pronunciation of individual letters varies from one language to another. Though many letters are often pronounced similarly, many also differ. It is thus necessary to learn the rules of orthography of each language.