Learn Turkish: İkinci güllü bukette hiç diken yok. - There are no thorns at all in the second bouquet with roses.

The suffix -lI creates adjectives meaning "with," "containing," or "having." Since gül means "rose," adding -lü (which follows 4-way vowel harmony) creates the adjective güllü, meaning "with roses" or "containing roses."

What is the difference between saying güllü buket and gül buketi?

Gül buketi is a noun compound that means "a rose bouquet" (a bouquet typically made entirely of roses). By using the -lI suffix instead, güllü buket specifically means "a bouquet with roses"—which heavily implies there are other kinds of flowers mixed in as well.

Why doesn't diken have a plural suffix if the translation says "thorns"?

When talking about a general category or concept of things existing or not existing (using var or yok), Turkish usually leaves the noun singular. Diken yok literally means "thorn is non-existent," which naturally translates to "there are no thorns" in English.

Does hiç always have to be used with a negative word like yok?

In statements, yes. Hiç means "at all" or "any" and acts as an intensifier. While diken yok simply means "there are no thorns," adding hiç makes it "there are no thorns at all." In a statement, hiç must pair with a negative verb, yok, or değil.