When writing on a wedding gift envelope, its important to keep in mind the tone and formality of the occasion. Here are some ideas from various sources on what to write on a wedding gift envelope in English:

• "Congratulations on your wedding/marriage!"
• "We/I love you! Congrats!"
• "Best wishes to you on this wonderful journey!"
• "May your joining together bring you more happiness than you can imagine!"
• "Wishing you all of the love and happiness!"
• "Heres to a long and happy marriage!"
• "May the years ahead be filled with love and joy."
• "Luck"
• "Love"
• "Happiness"
• "Wealth"
• "Health"
• "Prosperity"
• "Laughter"
• "Fun"
• "Joy"
• "Beautiful journey"

Remember to keep your message personal and heartfelt, and to choose wording that compliments your relationship to the bride and/or the groom.