Infojunkie, it´s hard to asses how much of English you learnt and your skills in general.
One thing is certain, you are in the right way, since you made a good piece of text.
Practice makes perfect, so from here on maybe you need professional help or something more to get it some notches up.
Anyway, your post was a little bit somewhat vague (at least to my thinking, of course). You never said to what end, if it is to travel, to get a job (e.g. job interviews), just to talk when you get to Orlando in your travels, to sing along some
music, to help you out into some line of work (medicine/law etc), to teach and the list could go on and on.
Maybe you have to make use it more, teaching somebody else, taking some serious test (for example IELT...), helping people out in EMB, there are lots of things in wich you may get sharper.
How can I test the actual extent of my knowledge about the English language?
Some sites have tests, and there are good books well designed and that even comes with CD, example the ones of Oxford and Cambridge. To cite a few.
If you have some monies you can take a course abroad, or you can go to the University back here and learn English to academic purposes.
Well, there will be plenty of ideas and suggestions soon let´s wait some come up.
In this site I saw these interesting description of levels:
Proficiency is the highest level we recognise.
You are fluent and rarely encounter English which you do not understand. However, it is always possible to improve by increasing your understanding of the nuances of the English language and by developing your vocabulary further.
-Study on any course up to and including Postgraduate level at an English-speaking university
-Work at an advanced level in an English-speaking environment
Advanced is the highest level most students attain without the total immersion of living in another country.
Your spoken English is both fluent and accurate. Your vocabulary is wide and you have a good knowledge of collocation, phrasal verbs, colloquial expressions and idioms. All common areas of grammar are familiar to you.
Study on any degree or diploma-level course at an English-speaking university
Work in an English-speaking environment
If you are at Upper-Intermediate level, you have an effective, but not perfect, use of English.
You can talk almost fluently and almost completely accurately. Everyday situations in an English-language environment do not worry you. You can take part in extended conversations or discussions and your vocabulary covers almost every circumstance. If you do not know a word you can almost always find a way of describing it. You have a knowledge of some idiomatic English, phrasal verbs, and colloquial expressions. You have studied all main areas of English grammar.
Study on some degree or diploma-level courses at an English-speaking university
Work on a work placement in an English-speaking environment
If you are at Intermediate level, you understand and speak English with some confidence.
You have the grammar and the vocabulary to talk and read about a wide number of subjects. You have some understanding of tone and style. You can assess and consciously improve your own pronunciation. You have studied all the main tenses and can confidently make sentences, question forms and clauses in all of them. You are beginning to look at phrasal and modal verbs.
Study on some courses at an English-speaking college
Enter university on a foundation course
Start to focus your English studies on specifics such as English for Business or Academic purposes
If you are at Pre-intermediate level, you have a good basic ability to communicate and understand, but you can make great improvement in all areas.
You can talk about many subjects and give your opinion on them. You can talk with confidence in the present, past and future simple tenses. You can perform tasks such as shopping, booking a hotel room, travel, and making conversation in English. Your grammar includes an understanding of adjectives, adverbs, comparatives, articles, possessives, and basic prepositions.
If you are at Elementary level, you can communicate in a very basic way, mainly in the present and past simple. Your vocabulary covers everyday useful subject areas.
and you can take an assesment test here (tough it is very short to assess anything at all...)