Thin-lipped. خَفِيفٌ الشَّفَةِ.

خَفِيفٌ الشَّفَةِ.
Thin-lipped.
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خَفِيفُ الشَّفَةِ يُقال لمن يكثر الكلام، أو يسرع إلى النطق، ولا يضبط لسانه؛ وقد يُراد به أيضًا من لا يتأنّى في كلامه.
وأقرب تعبير إنجليزي:
“He has a loose tongue.”
أي: «لسانه منفلت» أو «لا يحفظ لسانه».
ومن التعبيرات القريبة:
“He is quick with his tongue.”
أي: «سريع اللسان، سريع الرد والكلام.»
فإذا كان المقصود في المثل كثرة الكلام وعدم ضبط اللسان، فـ “He has a loose tongue” هو الأنسب.
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The expression "light of tongue" is used to describe someone who talks too much or speaks too quickly, without controlling their tongue. It can also refer to someone who speaks carelessly.
The closest English expression is:
"He has a loose tongue."
Meaning: "His tongue is loose" or "He doesn't hold his tongue."
A similar expression is:
"He is quick with his tongue."
Meaning: "He is quick with his tongue, quick to respond and speak."
So, if the proverb refers to someone who talks too much and doesn't control their tongue, then "He has a loose tongue" is the most appropriate.