I don't agree with you completely, but I understand what you're trying to say.
I don't neccessarily agree with what you're saying, but I understand why you'd feel that way.
Hello there.
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"I don't agree with you completely, but I understand what you're trying to say"は「完全には同意しないけど、言いたいことはわかる」という意味の文章です。
ほかにも"I don't neccessesarily agree with what you're saying, but I understand why you'd feel that way"は「あなたの言ってることに完全には同意しないけど、そう思う気持ちもわかる」という感じになります。
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Hope this helps.
日本 
