こんにちは。
with confidence で「自信をもって」という意味の表現です。「おすすめする」は recommend なので、recommend with confidence で「自信をもっておすすめする」になります。
「できる」という意味の can を加えて can recommend with confidence（自信をもっておすすめできる）と言えます。
例：
I can recommend this restaurant with confidence.
このレストランは自信をもっておすすめできる。
ぜひ参考にしてください。
If I were you, (and speaking from personal experience) I'd give that restaurant a try
If you give something your recommendation, it infers that you have first hand experience yourself. You could, alternatively, construct a conditional sentence ('If I were you....') in order to convey the idea that you yourself would go to this restaurant if you were in the same situation as the listener.
recommend'（勧める）は、自分も実際に体験したことがあるというニュアンスです。
また、条件文を用いて、「私があなたの立場だったら（If I were you....）このレストランに行く」と伝えることもできます。
If you want to say you would recommnd a restaurant then you can say 'confidently recommend' or 'highly recommend' to mean that you recommend it a lot and you enjoy it there
To be 'confident' means you are positive or certain about something
This restaurant comes with my high recommendation.
These sayings indicate that you have been to the restaurant and believe it to be very good! You are suggesting to someone else that they try this restaurant as well, because you know that it is good, and you really think they will like it too!
Also: "I really think you should try this restaurant!"
and: "You won't be disappointed!"
これらの表現は、話し手がそのレストランに行ったことがあって、すごくいいところだと思っていることを表します。そのレストランがいいところだと知っていて、相手もきっと気に入ると思っているので、そこに行ってみるよう勧めています。
また、次のようにも言うこともできます：
"I really think you should try this restaurant!"
［訳］このレストラン本当に行った方がいい！
"You won't be disappointed!"
［訳］絶対後悔しないから！
I have no reservations about recommending this restaurant.
I have no qualms about recommending this restaurant.
No reservations' just means you have no regrets about recommending the restaurant, or you have no reasons not to recommend it. 'No qualms' means the same as no reservations, so feel free to use them interchangeably.
No reservations'は、そのレストランを勧めることにためらいがないこと、そのレストランを勧めない理由がないことを表します。
'No qualms'も'No reservations'と同じ意味ですから、置き換えて使ってもらって大丈夫です。
Sometimes when you tell someone that you've heard that a restaurant is good, they may not be convinced but if you can explain that you personally went there and had a good experience then that person is more likely to believe you. I hope that this helps :)
I can recommend ... with confidence
自信を持って〜をおすすめできる
I can confidently recommend ...
自信を持って〜をおすすめできる
with confidence / confidently は「自信を持って」という意味の英語表現です。
アメリカ合衆国 
イギリス 
日本 
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