Hello, I also write in a mix of languages, in my case mostly Dutch (85%), English (10%), other languages 5% (German, Spanish, French). For my main language, Dutch, Qwerty is even worse than it is for English. Colemak is better, but not as good as it is for English.

By the way, it is hard to judge a layout by looking at one or two digrams, like how hard "th" is. There is much more to it, you need an algorithm to score layouts.

Your options if you don't want Qwerty: 
1. One of the "good"  layouts:  Colemak, Dvorak, AdnW, Carpalx
2. Variants of the good layouts (Workman, Norman for Colemak; Dvorak I/U swap etc.)
3. A custom, personal layout (Portuguese/English in your case).

Me, I calculated a custom layout. I know of three programs that you can use for this:
- AdnW. Look for Optimierer als C++-Quelltext .... etc and download it. (this means Optimizer as C++ source code). The website is in German, but the source code does have an English manual, it is fairly clear. The program is written, as you have guessed by now, in C++
- MTGAP. Website, source code, it is written in C
- Carpalx. Website and source code, it's written in Perl.

Steps:
a. Get the code, and maybe change some things. See the manuals, some things can be changed at runtime, other things need modiying the source and recompiling.
b. Make a text corpus that is representative of what YOU type
c. Feed the corpus to the program
d. Calculate your layouts
e. Make test layouts to try them out in real life (Autohotkey for Windows; xkb maps for Linux, at least that is how I do it)
f. maybe you want to play some more: change settings, assumptions, make it more alternating, more rolling, etc -> go back to step a.

Remarks:
- AdnW will give Dvorak-like layouts. AdnW will have nice alternation (at the expense of other criteria).
- MTGAP will give Colemak-like layouts. MTGAP will have lots of 'rolls' (at the expense of other criteria).
- Carpalx will give Carpalx-like layouts :-)  As far as I can see, Carpalx is very good at finger/ hand balance (at the expense of other criteria).

An easy, quick but rough online layout tester is patorjk

Good luck!

Edit: the analysers also have the option to "improve" one of the standard layouts, so you may start with Qwerty or Colemak or Dvorak or whatever and improve that, for instance by swapping max. 5 keys.

  Agreed (again) !

If/when I ever get lots of time, I'd love to build the ultimate keyboarding program/ website, that combines ideas from the existing ones:
* a tweakable optimizer, based on the ideas of mtgap, adnw, carpalx and others, with options such as:
- do you want to start off an existing layout (Colemak, Qwerty, Dvorak etc.) yes or no? If yes, which / how many letters should be kept in place?
- preferences for rolling, use of fingers (not to much load on left pinky for instance), alternation, liked and disliked key combinations and so on
- penalties and weights. Do you want layout that scores OK on all aspects, or layout is great for English but sucks at code? Should a sequence of 3 same-finger combos be a "show stopper"? In other words, what type of optimization do you want?
*with the option to generate AHK-files, XKB-keymaps, MS layouts etc. that you can run or install on your devices.
* a visual keyboard tester, looking like patorjk, in which you can easily compare layouts and try out new ones, with a nice graphical interface (drag & drop keys, etc.)
* a web tool for typing in different layouts , similar to mike kuhn's so you can try Colemak, MTGAP, or your custom layout in the browser.
* a Chrome/Firefox/etc extension for typing in a layout of your choice

Use cases:
- "I have some crazy layout idea, let's try it out in the browser. ..... Hey, I like this! Let me download the AHK-file so I can run it on my Windows PC"
- "I want to find the best layouts for my languages. Also, my left pinky is paralyzed so it should optimize for 9 fingers"
- "I hear Colemak is great, how does it look? Are the figures really that good?"
- etc.

Sounds like your thought process is similar to what I went through. I initially considered Norman too, being attracted by its easier-to-learn-ness, since it has fewer keys that change fingers. However what I hadn't fully appreciated back then is that keeping so many keys on the same fingers means not addressing Qwerty's annoying common same-finger keys such as LO and DE. To be fair, Norman does look quite in terms of easy-to-reach most common keys at least. But there are a lot of additional factors to consider when making a truly great layout design.

If you are concerned about TH (and also HE, which actually is worse), then you can't do any better than Colemak Mod-DH (in my very humble opinion!!)