Finding the right phrases is important so that you are able to express yourself clearly and concisely. When explaining to someone that you are struggling with phrases you could say any of the above sentences and all three would show that there are some parts of English you are still learning.
I find it hard to express myself.
I need to learn some more phrases
It is hard to choose the right phrases.
適切なフレーズを見つけることは、伝えたいことを明確・簡潔に表す上で、大切ですね。フレーズについて苦労していると伝えたいなら、上記の三例どれも使えます。三例とも、英語でまだ苦労している所があることを表します。
I find it hard to express myself.
（うまく自分の言いたいことが言えない）
I need to learn some more phrases.
（もう少しフレーズを身につけないといけない）
It is hard to choose the right phrases.
（適切なフレーズを使うのが難しい）
It's difficult to find the correct words, phrases, or expressions to express oneself in English.
When communicating in English, it is usually difficult to find the most appropriate words, phrases, or expressions to use.
Instead of using the verb to 'choose', you may vary that and use the verb to 'find'. So, instead of 'choosing' words, phrases, or expressions from among the pile you have stored in your brain, you may 'find' the most appropriate ones. The adjective 'appropriate' in this context means 'suitable'. When communicating either verbally or in writing, in English, you can only express yourself properly by using the most appropriate words, phrases, or expressions.
So, you may say to someone:
It's difficult to find the correct words, phrases, or expressions to express oneself in English.
or
When communicating in English, it is usually difficult to find the most appropriate words, phrases, or expressions to use.
動詞'choose'（選ぶ）の代わりに、 動詞 'find'（見つける）を使ってもいいです。ですので、語彙の中から単語やフレーズ、表現を'choose'（選ぶ）のではなく、最も適切なものを'find'（見つける）できます。この場合、形容詞'appropriate'は、'suitable'（適切な）という意味です。英語で話す場合でも書く場合でも、適切な（appropriate）単語、フレーズ、表現を使わないと、正確に自己表現をすることはできます。
It's difficult to find the correct words, phrases, or expressions to express oneself in English.
英語で適切な単語、フレーズ、表現を見つけるのは難しいです。
When communicating in English, it is usually difficult to find the most appropriate words, phrases, or expressions to use.
英語でコミュニケーションをとるとき、最も適切な単語、フレーズ、表現を見つけるのはたいてい難しいです。
It's hard to choose the exact words or phrase to use
Sometimes it's difficult in English to choose the right phrase or expression, especially among so many ways to say things. There are many phrasal verbs, slang and idioms that can make it confusing for one to choose which one goes in the right situation. Some are also quite similar to each other and so it can be tricky to decipher which one is best. Distinguishing the difference between the different expressions is the first step, then choosing which one is right or correct for want one wants to express. This can be tedious.
It's hard to figure out the right phrase when speaking English.
It's hard to pick out the best phrase when speaking English.
The two sentences you see provided above are excellent ways to express to your listener that it is difficult to choose the correct phrase when speaking English. In the first sentence you will notice the phrase figure out. This phrase means to understand. In the second sentence you will notice the phrase pick out. This means to choose. These phrases are common in our everyday conversation and they would make great additions to your vocabulary.
It's hard to find the right words when speaking English.
It's hard to express myself accurately when speaking English.
It's difficult to clearly express my thoughts using English.
hard (adjective) = difficult = not easy
express (verb) = communicate, show, put into words
accurately (adverb) = correctly
Other ways to express this thought:
It is a struggle trying to think of the right words to express myself in English.
I struggle with choosing the right words when speaking English.
struggle (noun) - a difficult thing to do
It is a struggle getting the kids up and ready for school in the morning.
Getting to work on time in the morning is a struggle because of the heavy traffic.
struggle (verb) - have a difficult time doing something
I struggle with getting enough sleep every night.
She doesn't struggle with learning foreign languages.
hard (形容詞) = 難しい = 容易でない
express (動詞) = 伝える、表す、言葉にする
accurately (副詞) = 正確に
別の言い方としては、例えば：
It is a struggle trying to think of the right words to express myself in English.
（英語で適切な言葉を使うのは難しいです。）
I struggle with choosing the right words when speaking English.
（英語で話しているとき、適切な言葉を使うのが難しいです。）
struggle (名詞) - 困難なこと
It is a struggle getting the kids up and ready for school in the morning.
（朝子どもを起こして学校に行く準備をさせるのは大変な仕事です。）
Getting to work on time in the morning is a struggle because of the heavy traffic.
（交通渋滞があるので、朝時間通りに出勤するのは大変です。）
struggle (動詞) - 苦労する
I struggle with getting enough sleep every night.
（毎晩なかなか十分な睡眠がとれません。）
She doesn't struggle with learning foreign languages.
（彼女は外国語の勉強が得意です。）
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