1.) 四葉のクローバーは基本、英語でもそのまま「四枚の[葉っぱ](https://eikaiwa.dmm.com/uknow/questions/51272/)」= "Four-leaf" と「クローバー」= "Clover"という単語を組み合わせて、"Four-leaf clover"と表現します。
2.) ただ、海外にも四葉のクローバー=[幸運](https://eikaiwa.dmm.com/uknow/questions/55000/)、というようなイメージがあるので"lucky clover"などと言われる事もあります。
*質問にありました「普通は葉っぱが３つですが４つを見つけたらラッキーと言われています。」という文章は上記の表現を使って、"Usually clovers have only three leaves but there are some that have four instead. People say that it's lucky if you could find a four-leaf clover."などと表現できます。
例：
I found a four-leaf clover yesterday.
私は昨日、四葉のクローバーを見つけました。
A clover usually has three leaves so if it has four leaves it is called a four leaf clover
A four leaf clover is said to bring you good luck by many and is seen as a lucky charm
A clover is usually called by the number of leaves it has. For example/; four leaf clover, three leaf clover and six leaf clover. Clovers, especially four leaf clovers, are considered lucky; for that reason, many times they are referred to as lucky clovers.
A clover with four leaves is called a "four-leaf clover". You can use this phrase in a sentence in the following ways:
-It is said that a four-leaf clover brings a person luck.
-If you pick up a four-leaf clover, then you are very lucky.
4つ葉っぱのついたクローバーは、"four-leaf clover"（四つ葉のクローバー）と言います。
文章の中では以下のように使えます。
【例文】
-It is said that a four-leaf clover brings a person luck.
（四つ葉のクローバーは幸運をもたらすと言われています）
-If you pick up a four-leaf clover, then you are very lucky.
（四つ葉のクローバーを見つけたら、とてもラッキーです）
A four-leaf clover, or lucky clover, is a tiny spring of a plant that is found in grassy areas in the UK. It usually has only three cloves and very rarely will you find one with four cloves. This is why a four-leaf clover is called lucky, it is believed to bring you good luck if you find one.
The four leafed clover is a rare variety of the very common three leafed clover. According to superstition, four leafed varieties of clovers bring good luck.
こんにちは。
「四つ葉のクローバー」は英語で four-leaf clover（フォーリーフクローバー）と言います。
clover が「クローバー」で、「四つ葉」は four-leaf と表現します。
「三つ葉」の場合は three-leaf になります。
【例】
I've never seen a four-leaf clover in my life.
「人生で一度も四つ葉のクローバーを見たことがありません」
I am good at finding four-leaf clovers.
「私は四つ葉のクローバーを見つけるのが得意です」
That's not a four-leaf clover, it only has three leaves.
「それは四つ葉のクローバーじゃないよ、三つ葉だよ」
ーー
ぜひ参考にしてください。
A clover that has four leaves is known as, 'a four leaf clover'.
"Mary won the lottery sortly after having found a four leaf clover in her garden."
「四つ葉のクローバー」は 'a four leaf clover' といいます。
"Mary won the lottery shortly after having found a four leaf clover in her garden."
（メアリーは庭で四つ葉のクローバーを見つけた直後に宝くじを当てた）
日本 
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アメリカ合衆国 
イギリス 
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