Resolved questions
Can a German speaker still understand me?

Hello,

It is possible that we understand some of that sentences but not all...

For example your sentence:
"Ich bin mit meine freunds nach London gefahren." is unclear, mostly because "meine" is also in a wrong casus. It turns unclear who and how many people you exactly mean by "Freunds".

"Ich esse ein gross Apfelsine in das Flughafen." is still understandable, but of course it sounds strange to us Germans anyway.

I think, if you learn all the other verb tenses, it is not too much effort to understand the gender rules and the cases, plural and so on after all. I know, for a student it is hard to remember all of them at the beginning but I am sure due practise you are able to manage them. As you learn all the tenses of the verbs, I recommend to study nouns with the gender and plural. After a while of doing this, you will see similarities and it won't seem that random for you any more.

Even in your two examples, the sound of this sentences would not cause a good reaction from a native speaker.

And one more thing: It is ok to make mistakes sometimes, we would not be mad about that, even a native speaker does not speak 100%-ly perfect grammar. I just think to ignore grammar/language rules on purpose is not really helpful.

Beste Grüße

Tony

You will probably be understood most of the time, but (I don't know how to phrase this more politely) you will sound like an idiot.

If you're on vacation in Germany and use this kind of broken German, people probably won't mind. If you are, say, looking for a job, please don't try to do this in a job interview. Your chances will be a lot better if you put in some effort to use proper grammar. Even if you still make mistakes.