Fix typos

knowledges ->
knowledge
Fix typos

User agents (...) sends -> User agents (...) send
to the user agent -> to the user agents
Add a missing comma
Fix a typo

experiences how setup ->
experiences to  setup
Use a plural

Prepare a configuration file  ->
Prepare   configuration files
Add a missing comma
Add a missing "with"
Add a missing "the"
Fix a typo

focus an ->
focus on
Fix a typo

21th ->
21st
Remove an extra "to"
Fix typos

a <-> an
Fix a typo

is larger than ->
is larger than or equal to
Update .po files and .md files for ja