心里很难过

这个星期六我出发去北京。我觉得我的汉语很不好，因此我很难跟中国人聊天。
我没有电词典，这对于我来说是件不好的事
电词典能帮我学习汉语。 
我要先学好在飞机场的会话用语。
我不想离开妈妈和姐姐，我已经开始想她们。
尽管有一些难处， 但是我非常想游览中国也想试一试跟中国人聊天。
。。。 要准备行李：一个皮箱一个背包 。

加油练习汉语吧，我想你一定会学得好的。

心理很难过

这个星期六我出发北京。
我觉得我的汉语很不好，我不会跟中国人聊天。
我没有电子词典，这是一件不好的事。
电子词典更帮我。
我要学好“飞机”这个词。。。
我不想离开妈妈和姐姐，我已经开始想他们。
难过，我非常想看中国也想试一试跟中国人聊天。
。。。 要准备行李：一个皮箱和一个背包 。

心理很难过

这个星期六我出发北京。

这个星期六我出发去北京。This Saturday I am leaving for Beijing.   or   This Saturday I am setting out to Beijing. "leaving" and "setting out" match the word "出发", and "for" and "to" match the word "去". "出发" only has the sense of "leave", so when you want to add words about place, no matter the place you leave from or leave for,  you have to add a recording Chinese word for it. "leave from" means "从。。。出发"， and "leave for" means “出发去。。。”
我觉得我的汉语很不好，我不会跟中国人聊天。

我觉得我的汉语很不好，无法（没办法，不能）和中国人聊天。“不会”has two meaning. One is "wouldn't", and another is "cannot". When it means "cannot", there must be a word describing a skill or ability right after it. For example "我不会洗碗（I cannot do dishes）"，“我不会唱歌（I cannot sing）”. But when you add some words between 不会 and the skill, the meaning may change to "wouldn't". For example "我不会帮你洗碗（I wouldn't help you to do dishes）" “我不会和你去唱歌（I wouldn't go to sing with you）”. So most of time we use another word to express ourselves in case others may misunderstand. There are other words meaning "cannot", such as "不能","无法"，and "没办法". And most of time, when we want to express the meaning of "wouldn't", we use "不会". 
我没有电词典，这是不好。

我没有电子词典，这样不好。“电”is used to limit or describe the function or character of something only when  those things have to work with electricity. But for other things, such as translator and electronic book, they don't really need electricty directly. They are just based on electronic device. In this situation, we use "电子" to distinguish them from normal translators and books. Also we call all of them as "电子产品" which means electronic production. "电子XX" is used to specify the character of things. "电XX" means those things really need electricity.

      About "be". When you use "be" in a sentence, you can put adjective word or noun after it. When you put noun after that, you should translate "be" as "是". For example: I am a teacher. 我是一个老师. But when you put adjective words after that, you can not always translate it as "是". If you want to translate it as "是", you can not omit "的" at the end of the adjective word. For example, you can say "这是美丽的", but you cannot say "这是美丽". Instead you can say "这很美丽".  In your composition, you can say "这是不好的" (grammarly correct), but you cannot say "这是不好". Most of time, we don't use "是", but use "很" or other words instead. For example: 他很帅 is right, but you cannot say 他是帅.  In this situation, "很" doesn't really mean "very". It is just a custom of Chinese in speaking.

电词典更帮我。

电子词典对我有很大帮助。（Electornic translator helps me a lot）“更”can be only used when you compare two or more than two things. For example: 比起字典，电子词典对我有更大的帮助。Comparing to dictionary, electronic translator helps me more. 比起哥哥，我更高。Comparing to my elder brother, I am taller.  
要学好飞机的词。。。

我要学好和飞机相关的用语 （I want to learn the saying about plane well.）I am not sure what you exact meant by this sentence. I guess maybe you want to say "I want to learn how to communicate about my flight". If you want to express that, you can say "我想学习关于飞机场的日常用语". I know it is a little tough for you to express this. Bcz Chinese is really specific, unlike English, which is abstract most of time. You can use "get","make","take"...as a lot of verbs, but in Chinese you have to say specific verb. For example: I can not make it. In Chinese, we have to change "make" to exact verbs. When you can not sing, can not finish the work, or can not go to the date, you all can say "I cannot make it". But in Chinese, we have to say "我唱不了"，“我完不成这项工作”，“我不能去约会”. You will know more as the time goes by. :)
我不想离开妈妈和姐姐，我已经想他们。

我不想离开妈妈和姐姐。我已经开始想念他们了。"想念" is an action may last for long time, so what really happened is "You started that action". “了" means the action already happened. In Chinese, "了" and "过" are about past tense and perfect past tense, and "着" can be viewed as the form "doing sth".  
难处 我非常想看中国也想试一试跟中国人聊天。

Sorry I am not sure what you meant by "难处". You can write it in English and I will correct it for you if you want. 我非常想看中国，也想试一试跟中国人聊天。 In this sentence, there are two different verbs, and both of them have their own objects. So you should use a camma to seperate them. 
。。。 要准备行李：一个皮箱一个背包 。

我要准备行李：一个皮箱和一个背包。和：and