I'm not sure but I would say : none
horizontal, zébré, zazou, azimuté
There are no adjectives beginning with the letter z that describe a shy person.
No adjectives end in i. Actually, no words in English end in i.
not all adjectives, but most adjectives from nouns do end in -ly, also adverbs from adjectives.
zany !
analyzablecognizableenzymaticfreezablehazardoushorizontalmagnetizablenonhazardousorganizationaloverzealousprotozoicquizzicalrealizablerecognizableschizophrenicsizablesizeablesqueezabletrapezoidalunrecognizablezealouszestfulzodiacalzonalzoologicalzoophyticzygotic
there are too many adjectives in French to give it a try. That wouldn't be much use anyway: with just a few hundred words (not only adjectives), you will be perfectly undertood by French speakers.
zealous
zaftigzanyzappedzappyzealouszerozestfulzestyzingyzippyzonked
icyjumpykindlumpymaniacalnewoptimisticpopularquietrambunctioussoftturbulentuglyvaguewetxenophobicyouthfulzesty
in spanish most feminine adjectives end with the letter A
There are a great many French adjectives that begin with the letter B. Belle is one French adjective that means beautiful.