Everyone struggles learning a new language. At one point in time, you even struggled to learn English as a babbling, grammatically challenged toddler. Since no one joins the world as a master of even their native tongue, you can take heart in the biological fact that we are hard-wired for linguistic domination.
If you're passionate about studying new languages, you will achieve fluency with time and effort -- and by applying practical strategies to the common problems you're destined to come across. In my own experience, I've studied Spanish, Latin, Chinese, and Arabic and at some point picked up smatterings of Portuguese and Amharic, so I feel your pain.
Persist through these natural challenges on the road to fluency and you'll someday gain all the benefits of being bilingual.
Problem: Mastering a Comprehensive Vocabulary
In order to speak another language, knowing what to call things -- especially things you can't just see and point to -- is the essential first step towards speaking in any language. However, vocabulary is often spotty from classroom learning, which tends to focus on memorizing lists of words in the target language and their definitions in English. This leads to the common frustration of knowing how to talk about the constitution in French, but not knowing how to say useful things like cupboard or butter knife.
Strategy: Try Alternative Methods of Building Vocabulary
There are a few ways to improve vocabulary, all of which include learning in context. When I studied Chinese, for example, I had a five subject notebook and dedicated one of each section to a topic, depending on my level and interests, i.e. food, household items, politics, finance, and music. Then, I would spend a few weeks focused on learning words related to these five main subjects and categorizing them separately. When I reviewed vocabulary, I'd review them by topic. I would also build lists of synonyms, so whenever I defined a word, I'd list a few other synonyms in the target language so my vocabulary would become more sophisticated and diverse.
There's also the old trick of building vocabulary in a physical space, like putting up note cards all over your kitchen and bathroom to label things in the target language. Defining words in the target language instead of English is also an excellent tactic that helps you rack your brain for words you already know to describe the new word.
Problem: Incorrect "Semantical Usage" of Vocabulary
Also known as "using the correct word in the wrong context," or using a word in a way that makes sense but a native speaker would never put it quite the creative way you have. This is a more advanced-stage problem in language learning that occurs once you're already at a conversational level and is probably related to the origins of your vocabulary using the antiquated "target language: English definition" method.
Strategy: Increase Your Exposure to Native Speakers and Phrase-Based Vocabulary Work
The first easy adjustment to do is an extension of the vocabulary techniques described above. Once you've mastered grouping vocabulary by topic and defining it in the target language, begin to add phrases that contain that word to its section. Progress to studying phrases, especially common sayings, instead of words singled out of their linguistic habitat.
The next strategy is to drastically increase the amount of time you spend listening to and reading content written by native speakers. Since you're already having conversations, you're ready for this next big step. It may seem counterintuitive to listen more since the problem is related to your speaking abilities, but think of how a baby learns a language: by listening, catching on to context, and repeating. Children listen to native speakers (adults) for years before they start speaking. Do the same when you're learning your second or third language. Watch movies and TV with a notebook in hand and jot down useful phrases you hear. Follow Instagram accounts in Italian to learn Italian, read Brazilian fashion blogs, and follow Japanese Twitter accounts.
Problem: Mastering a Wildly Different Writing System
For learners of languages like Chinese and Japanese, you'll soon realize the reason these languages are notoriously difficult is not that they're all that hard to speak or understand, but because the writing system is unbelievably complex. Languages with a different alphabet like Arabic, Korean, or Russian will also come up against the need to recognize different shapes and swirls and the new sounds they produce.
Strategy: Repetition, Read, Write, and Review
Children in China and Japan are no different than children anywhere else, they've just been repeatedly exposed to a different language system from a young age. You just have to catch up and you're a few years behind. Start with repetition: writing every Chinese character 50 times on a white board (saves paper). It's brutal, but eventually, it sticks.
Once you have a foundation of maybe a thousand basic words, progress to reading anything you can get your hands on -- with a dictionary nearby. A friend of mine ordered the Harry Potter series in Chinese and took about a year to read the first one, but she did it. She wrote down all the vocabulary she learned, categorized it, and memorized it.
Finally, start writing. Try keeping a daily journal in your target language and write a few sentences about your day every night before bed. Have your teacher or a native-speaking friend review and correct it for you once a week. You'll build vocabulary relevant to your daily life, make fewer grammatical mistakes over time, and practice those difficult characters.
Problem: Getting Rid of a Foreign Accent
It's not that big of a deal and one of the least important things in language learning because you should strive to understand and be understood above all. But for advanced learners and fluent conversationalists, this can become frustrating over time.
Strategy: Try Immersion and Careful Listening
This is mostly a matter of immersion. If you're only speaking a couple hours a day in the target language and going back to English, you'll never lose your accent. In my experience, I've only improved my accent once I was speaking non-stop with native speakers day in and out and unconsciously picking up their pronunciation. Listening intently to the native speakers around you and hiring a tutor to focus exclusively on your pronunciation is another way to make strides towards sounding more local.
Problem: Listening Comprehension at Native Speaker Speed
Sometimes you can understand everything in classroom exercises but can't keep up with how fast native speakers speak. For example, the first week in Lebanon after two years of painstaking Arabic work is enough to make a lot of language students give up.
Strategy: Consume Media in the Target Language
For now, the most important thing is time and consistency. Download TV and movies in your target language, listen to the radio and watch the local news. It will get better. Don't worry about getting every word, just keep listening to entertaining things and try to get the gist of what's going on. I used to watch movies in Chinese one night without English subtitles and the next night without them. I also committed to watching CCTV news every night and just letting my head spin. Eventually, along with diligent classroom work, I started to understand more and more.
Language Learning is a Matter of Time, Effort, and Exposure
Most of the intimidating multi-linguists you know are not smarter than you. They have simply had more exposure to the languages they speak. To overcome the difficulty of learning any new language, your job is to craft an environment that maximizes your familiarity with it and stay committed to active work in all four areas of the language reading, writing, speaking, and listening. Do this and you will become fluent!