Enable i18n plugin, configure, and prepare for switch to Weblate (#637)

Removes Lektor alternative content, moving translations to gettext .po files so they can be 
handled by Weblate.

Explclictly excludes some "rapidly moving" content (such as blog content) from translation.

---------
Co-authored-by: Russell Keith-Magee <[email protected]>

Author: kattni

.gitignore

@@ -7,3 +7,5 @@ venv*/
 .vscode/
 .envrc
 .idea/
+contents+*.lr
+i18n/_compiled

BeeWare.lektorproject

@@ -83,6 +83,7 @@ locale = fa_IR
 lektor-github-repos = 0.1.1
 lektor-gravatar = 0.1.3
 lektor-markdown-admonition = 0.3.1
+git+https://github.com/beeware/lektor-i18n-plugin@v0.5.1 =
 
 [servers.ghpages]
 target = ghpages://beeware/beeware.github.io?cname=beeware.org

babel.cfg

@@ -0,0 +1,2 @@
+[jinja2: **/templates/**.html]
+encoding = utf-8

configs/i18n.ini

@@ -0,0 +1,5 @@
+content = en
+translations = ar, cs, da, de, es, fa, fr, it, ko, pl, pt, tr, zh_CN, zh_TW
+i18npath = i18n
+translate_paragraphwise = True
+url_prefix = https://beeware.org/