I translated en.yaml file, rename it to mk.yaml. Everything works good, I have my bilingual site, except in the menu I can see and click English, to go to English site, but drop down for “Macedonian” is empty. I can click on it and go to Macedonian site. I am using academic theme. Any help, please?
And picture of problem
If you can share your repo someone might help more easily
Sure 
I suspect this area is the problem area:
It appears to be relying on languages present in i18n which seems different from the usual. I’m ranging over available translations in another site like this:
{{ "<!-- ENTERING partial nav-main.html -->" | safeHTML }}
<nav class="bt bb b--black-20 tc center ma1 mb0 bg-dark-teal">
{{ $currentPage := . }}
{{ $currentLang := .Site.Language.Lang }}
{{ range .Site.Menus.main }}
<a class="f6 f5-l link bg-animate white-90 hover-bg-darker-teal hover-teal dib pa3 ph2-l {{if $currentPage.IsMenuCurrent "main" . }}yellow bg-darkest-teal b{{else}}white-80{{end}}{{ if eq $currentLang "en" }} athelas{{ end }}" href="{{ .URL | absLangURL }}">{{ .Name }}</a>
{{ end }}
{{ if .IsTranslated }}
{{ range .Translations }}
<a class="f6 f5-l link teal bg-near-black-teal bg-animate hover-dark-yellow hover-bg-dark-blue grow no-underline br-pill ph2 pv1 mb2 dib" {{ if eq $currentLang "ja" }}lang="en"{{ else }}lang="ja"{{ end }} href="{{ .Permalink }}">{{ .Site.Language.Params.languageName }}</a>
{{ end }}
{{ else }}
{{ if eq $currentLang "en" }}
<a class="f6 f5-l link teal bg-near-black-teal bg-animate hover-dark-yellow hover-bg-dark-blue grow no-underline br-pill ph2 pv1 mb2 dib" lang="ja" href="/">日本語</a>
{{ else }}
<a class="f6 f5-l link teal bg-near-black-teal bg-animate hover-dark-yellow hover-bg-dark-blue grow no-underline br-pill ph2 pv1 mb2 dib" lang="en" href="/en/">English</a>
{{ end }}
{{ end }}
</nav>
{{ "<!-- LEAVING partial nav-main.html -->" | safeHTML }}
Thank you @RickCogley for answer. Obviously, I am n00b enough in html, so I’m doing something wrong. Now I have two menus, but dropdown is still empty. 
Edit: without code you suggest, if I change “mk” (Macedonian) to “ru” (Russian) all works flawlessly.
I solved it w/o any special code.
Just add
"mk": "Македонски"
in languages.yaml located in …\themes\academic\data\i18n