htaccess multi language site with sub directories, and default 301 - .htaccess

Question

I am having some issues setting up my htaccess to allow multiple languages utilising the sub directory method eg:
http://www.domain.com/en/
http://www.domain.com/sw/
http://www.domain.com/ie/
Also to complicate things, the project isn't currently live, its on a dev server. For example, I am currently accessing the project at:
http://dev.domain.com/devname/projectname/
And I want the above to automatically 301 redirect to:
http://dev.domain.com/devname/projectname/en/
Here is my htaccess:
Options +FollowSymLinks -MultiViews
RewriteEngine on
# ----------------------------------------------------------------------
# MULTI LANGUAGE SUB DIRECTORY
# ----------------------------------------------------------------------
RewriteCond %{REQUEST_URI} !^/(en|sw)/
RewriteRule ^(.*)$ en/$1 [R=301,L]
# ----------------------------------------------------------------------
# Rewrite rules
# ----------------------------------------------------------------------
## CASE STUDIES ##
RewriteRule ^casestudies/([^/\.]+).html$ index.php?controller=contents&method=viewCasestudy&link=$1 [L,QSA]
## PRODUCTS ##
RewriteRule ^products/([^/\.]+).html$ index.php?controller=contents&method=viewProduct&link=$1 [L,QSA]
RewriteRule ^([a-z{2}]+)(/)?$ index.php?controller=contents&method=viewHome&lang=$1 [L,QSA] # Default load
RewriteRule ^(/)?$ index.php?controller=contents&method=viewHome [L,QSA] # Default load
The above will actually redirect to:
http://dev.domain.com/home/webserver_dir/devname/projectname/en/
..and if I use RewriteBase it seems to just goto...
http://dev.domain.com/en/
So my question: How do I get the language URLs working correctly relative to the directory its in on my dev server, and then ideally will work when it goes live without any environment specific rules.
Bonus question: Do I need to add the ([a-z{2}]+) bit in front of all my subsequent rewrite rules or can I have a catch all that will effect all further rules?
EDIT -----------------------------
I have reduced it down to the following as suggested...
Options +FollowSymLinks -MultiViews
RewriteEngine on
RewriteBase /devname/projectname/
RewriteCond %{REQUEST_URI} !^/(en|sw)(/|$) [NC]
RewriteRule ^(.*)$ en/$1 [R=301,L]
RewriteRule ^([a-z]{2})/?$ index.php?controller=contents&method=viewHome&lang=$1 [NC,L,QSA] # Default load
... but now its redirecting to http://dev.domain.com/devname/projectname/en/en/en/en/en/en/en/en/en/en/en/en/en/en/en/en/en/en/en/en/en/, any ideas?

Answer 1

Have you tried the answer in the following link? It should do what you're trying to achieve.
Endless Redirect Loop by htaccess rules multi language
RewriteEngine On
RewriteBase /
# empty url -> redirect to en/
RewriteCond %{QUERY_STRING} !lang=(en|de)
RewriteRule ^$ en/ [R=301,L]
# url is ONLY '/en' or '/de' -> redirect to /en/ or /de/ (adding slash)
RewriteRule ^(en|de)$ $1/ [R=301,L]
# now all urls have en/ de/ -> parse them
RewriteRule ^(en|de)/(.*)$ $2?lang=$1&%{query_STRING} [L]

Answer 2

If .htaccess must not change
Change your <VirtualHost> configuration for your DEV server project as
<VirtualHost *:80>
ServerName dev.domain.com
ServerAlias project.domain.com
DocumentRoot "/home/webserver_dir/devname/projectname"
</VirtualHost>
These changes would typically go in your httpd-vhosts.conf file. Your .htaccess files would now have
RewriteBase /
to mark root as your base directory for both your development and live servers.
If you're trying to version your projects or test multiple projects on the same dev host, then you would have to incorporate the naming scheme into the domain names instead of the URL path. For example,
<VirtualHost *:80>
ServerName dev1.domain.com
ServerAlias project1.domain.com
DocumentRoot "/home/webserver_dir/dev1/project1"
</VirtualHost>
<VirtualHost *:80>
ServerName dev2.domain.com
ServerAlias project2.domain.com
DocumentRoot "/home/webserver_dir/dev2/project2"
</VirtualHost>
The bottom line is that you can not have the same .htaccess file rules working untouched with different deployment directories unless you resort to mod-rewrite way of if-else mumbo jumbo which would just be added clutter once you've gone live.
For the rules to work transparently, Apache must only see and apply the rules on what's going live (the content that comes after /devX/projectX/ directories) which is what shifting the DocumentRoot does here for us.
If minimal mods to .htaccess are okay
Not everyone has access to Apache's .conf files. Certain hosts out-rightly reject requests to modify them. Which is why, if they have at least kept mod-rewrite enabled, a lot of website's settings can be tinkered with. One of them is to use RewriteBase to handle the different deployment directories.
So, if you keep RewriteBase / on live but change it to RewriteBase /devX/projectX/ for development, most of your RewriteRules should work as is. So, /devname/projectname/ should correctly redirect to /devname/projectname/en/.
Your use of ([a-z{2}]+) is incorrect. You probably meant ([a-z]{2}) to capture exactly two letters. If you meant to capture two or more, it would become ([a-z]{2,}). So, your default load rewrite would become
RewriteRule ^([a-z]{2})/?$ index.php?controller=contents&method=viewHome&lang=$1 [NC,L,QSA] # Default load
You're correct to assume that you would need this regex for all subsequent rules or they would fail to match. So, your RewriteRule for casestudies won't work. A simpler way to not care about the language prefix is to drop the ^ start of URL path anchor as
RewriteRule /casestudies/([^/\.]+).html$ index.php?controller=contents&method=viewCasestudy&link=$1 [NC,L,QSA]
RewriteRule /products/([^/\.]+).html$ index.php?controller=contents&method=viewProduct&link=$1 [NC,L,QSA]
Your last RewriteRule matching ^(/)?$ isn't required because you're already doing a 301 redirect for all URLs with no language directory prefix to /en/$1 above, which should ideally be
RewriteCond %{REQUEST_URI} !^/(en|sw)(/|$) [NC]
RewriteRule ^(.*)$ en/$1 [R=301,L]
Otherwise, /en would get redirected as well to /en/en.