Restaurant is a French word. In French it is pronounced something like "REStORAn". Here t and n are pronounced with very light touch. In case of JOEL, (O+E) is a dipthong and it is pronounced something like "oye"and Joel is prounced like Joyel (O + Y + E) is called triphone.
Please go through the following to know more about silent use of letters in English.
Use of silent E
Get and Gat(e), Fat and Fat(e), Flat & Plat(e)
When silent E occurs in an English word, it converts a vowel to its "long" equivalent. If English were spelled with the traditional Romance language vowel values of the Latin alphabet, often these vowels would be written with another letter entirely. Moreover, alternatives exist in English for most spellings that use silent E. Depending on dialect, English has anywhere from thirteen to more than twenty separate vowel sounds (both monophthongs and diphthongs). Silent E is one of the ways English spelling is able to use the Latin alphabet's five vowel characters to represent so many vowels.
Traditionally, the vowels /ei (as in bait beet bite boat beauty) are said to be the "long" counterparts of the vowels /æ (as in bat bet bit bot but) which are said to be "short". This terminology reflects the historical pronunciation and development of those vowels; as a phonetic description of their current values, it is no longer accurate. The values of the vowels these sounds are written with used to be similar to the values those letters had in French or Italian. The traditional "long vowels" also closely correspond to the letter names those vowels bear in the English alphabet, and the letter name is usually an accurate guide to the value of the vowel that is affected by silent E.
This variety of vowels is due to the effects of the Great Vowel Shift that marked the end of Middle English and the beginning of Early Modern English. The vowel shift gave current English "long vowels" values that differ markedly from the "short vowels" that they relate to in writing. Since English has a literary tradition that goes back into the Middle English period, written English continues to use Middle English writing conventions to mark distinctions that had been reordered by the chain shift of the long vowels.
When final 'e' is not silent, this generally requires some sort of indication in English spelling. This is usually done via doubling (employee: this word has employe as an obsolete spelling). When the silent e becomes a part of an inflection, its non-silent status can be indicated by a number of diacritical marks, such as a grave accent (learnèd) or a diaeresis (learnëd, Brontë). Other diacritical marks can appear in foreign words (compare résumé with nativized resume).
The sounds of the 'a' group are some of the more dialectically complex features of contemporary modern English; the sounds that can be represented in modern English by 'a' include /æ/.
The 'e' group
Silent E typically moves 'e' to /iː/. This change is generally consistent across all English dialects.
The 'i' group
For the "long vowel" represented in written English by 'i', the effect of silent E is to turn it into a diphthong / In some dialects, this diphthong is affected by the voiced or unvoiced quality of the following consonant so that it may be closer to see Canadian raising.
The 'o' group
Short 'o', in contemporary English, tends to fall in with short 'a' and to share some of the complexities of that group; depending on dialect, the written short 'o' can represent . The usual effect of silent E on written 'o' is to fix it as a long o sound. In several dialects of English, this long realized as a diphthong and in some forms of southern British English, the leading element is centralized further, yielding . All of the sounds in the previous sentence are in free variation with one another.
The 'u' group
Silent E generally turns the sound written as 'u' to its corresponding long vowel /juː/, although there are exceptions depending on dialect (see yod-dropping). Initial long 'u' as in use is almost always subject to iotacism.
Silent E and consonants
Silent E also functions as a front vowel for purposes of representing the outcome in English of palatalized sounds. For example:
Truly silent E
In some common words that historically had long vowels, silent E no longer has its usual lengthening effect: come, done. This is especially common in some words that historically had 'f' instead of 'v', such as give and love; in Old English, /f/ became /v/ when it appeared between two vowels (OE giefan, lufu), while a geminated 'ff' lost its doubling to yield /f/ in that position. This also applies to a large class of words with the adjective suffix '-ive', such as captive, that originally had '-if' in French.
Some English words vary their accented syllable based on whether they are used as nouns or as adjectives. In a few words such as minute, this may affect the operation of silent E: as an adjective, minúte has the usual value of 'u' followed by silent E, while as a noun mínute silent E does not operate. See initial-stress-derived noun for similar patterns that may give rise to exceptions.