I recommend the [Grammarly blog] (https://www.grammarly.com/blog/).

https://www.grammar-monster.com is great

Kindle, Kobo, iBooks, etc. Read lots of stories in English.

I also tried dozens apps to improve my English level

And personally I totally agree that GetFluently is the best app to study and practice English

Its real life conversational practice and feedback on your speech are the killer features which helped me a lot to go from intermediate to upper-intermediate level

Hey there! I’ve been an ESL teacher for 10+ years, 1 on 1, corporate, immersions etc. Recently I’ve put together a doc with the apps and resources I’ve found most helpful for students of any level. Hit me up on the DMs in case you’re interested!!!

Duolingo

Great list, man. I love your recommendations.

Do you know any app to practice listening? I know it’s better to listen to music or watch multimedia in English, but I need other ways.

I appreciate your response.

Great list, thanks for sharing!

I’m also trying to reach an advanced level and I would recommend Netflix. It’s not a learning app but you can find thousands of interesting movies and TV shows in English. Unlike most Egnlish apps Netflix at least not boring, and you don't drop it on the first week :)

Absolutely Hellotalk. ��

DUoLiNgO

NoRedInk (website) is a very useful tool, in my opinion.

Haven't tried them all, so can't say for certain, Lingodeer is pretty good though. It's definitely not Duolingo.

I have a resource guide here. r/Korean also has a resource guide here (I didn't know about this when I made my guide :p)

TL;DR if you don't want to leaf through both these guides:

If you're looking for a grammar app specifically -- Lingodeer, as suggested

If you're looking for an app not focused on grammar -- Drops is good

If you're looking for a grammar resource that doesn't have to be an app -- TalkToMeinKorean is the best hands down

If you’re looking for an app specifically I recommend Lingory. It’s probably one of the best apps for Korean that I’ve personally ever encountered.

Have you mastered hangul yet?

If you are not in a hurry and wish to start from the basics, I recommend using LingoDeer app. It teaches you not only grammar, but also vocabulary and phrases all together.

You can use Tae Kim and afterwards google grammar points as you encounter them (Japanese grammar is for the most part very easy to google).

I'm aware paid apps probably are better

They are not.

I like to use bunpro.jp for this. You can look up grammar for free and get explanations plus example sentences. You only need to pay if you want to use their SRS.

For looking up grammar, googling works pretty well using this pattern:
japanese .

The "japanese" spelled in latin characters sorts out all the japanese-only content and usually brings up learning sites. You can also use "japanese grammar" without the quotation marks instead. As grammar term, you can usually use the kana part of what you don't understand. This still works quite often, even though you're using too many or too few characters. I used this hundreds of times myself.

If you're also looking for a free grammar resource: I made a free anki deck that teaches everything from zero, someone else already mentioned it. Here's the link: https://ankiweb.net/shared/info/911122782

I think the jlab deck is really good for it, it is based on tae kim and personally i find it easier to learn grammar by repeated examples

I prefer renshuu to bunpro. Bunpro requires registration to use the app and gives a month of free pro immediately, which is off putting to me cause I want to use the free month at my convenience, not immediately after registering...

Renshuu is just easier and while you need to pay to do proper study, the grammar lookup is easy. In the side menu: resources -> grammar library.

For proper grammar study I would use Tae Kim's site.

For a fun way to look at various quirks of the English language, I recommend dipping into Grammar Girl. Start at the oldest material, because that tends to deal with more basic concepts, and pick things that look interesting. It's not a structured course, and you definitely don't need to read/listen to/watch everything,

Take comfort from the fact that you already know (and care) more than the average native speaker.

Never be embarrassed to learn something new!

Something they showed us American kids a lot was “ schoolhouse rock “, any of the ones on grammar should be exactly perfect!

** schoolhouse Rock - Nouns! **

There are also ones on adverbs and pronouns and probably some other ones just search schoolhouse rock on YouTube dude !!

Good luck on your learning journey

From your paragraph, your English looks very good. Other than the suggestion of using the library to look for grammar refresher books, I would say maybe read some books in English.

Also, please tell me you use “this” and “these” appropriately. 😂

"I'm embarrassed by the fact I'm not entirely fluent in 4 languages" is certainly an interesting insecurity to have.

If your library has this book https://www.amazon.com/TIME-Kids-Grammar-Rules-Editors/dp/1603209549

I'm in my 30s and I picked it up to refresh my grammar in prep of learning a new language and it's quite helpful. It gives a lot of realistic examples and down to earth explanations as well as comparison on how a sentence changes based on punctuation. Best part is it's not from square one. So you're not trudging through things you already know. It assumes you know how to speak and read and this book generally helps you to write.

in addition to what u/Buck11235 said, the book D.I.Y Welsh by D. Geraint Lewis is a really accessible guide to Welsh grammar.

I don't think any of the apps are really good at teaching Welsh grammar. SaySomethingInWelsh is great at teaching you how to speak but it explains very little of the grammar.

If you want grammar instruction, I think you need either classes or some written materials. Something like the Dysgu Cymraeg course materials that you can dowload for free from them might be good, or a book like Welsh in 12 Weeks by Julie Brake.

Also check out the grammar resources in the wiki.