How to use:

Copy the file migrate_from_trac.rake in the directory lib/tasks, overwriting the original file.

Use the description of migration from the site: http://www.redmine.org/wiki/redmine/RedmineMigrate#Trac
Additionally, for the migration of svn, use the command:

rake redmine:migrate_from_trac_svn RAILS_ENV="production"

Additional information is on the link:
http://www.redmine.org/issues/5035

Tests:
---
# RAILS_ENV="production" script/about

About your application's environment
Ruby version              1.8.7 (x86_64-linux)
RubyGems version          1.3.4
Rack version              1.0
Rails version             2.3.5
Active Record version     2.3.5
Active Resource version   2.3.5
Action Mailer version     2.3.5
Active Support version    2.3.5
Application root          /home/redmine-trunk
Environment               production
Database adapter          postgresql
Database schema version   20100323105501
---

   Trac -> DB:      sqlite3
          Charset:  UTF-8
          Language: Russian
          
Redmine -> DB:    postgresql, mysql
           Charset: UTF-8

migrate project1:
---
Migrating components                     [******************************] 100%  
Migrating milestones                     [******************************] 100%  
Migrating tickets                        [******************************] 100%  
Migrating wiki                           [******************************] 100%  

Transform texts to textile format:
   in Wiki pages                         [******************************] 100%  
   in Issues                             [******************************] 100%  
   in Milestone descriptions             [******************************] 100%  

Components:      7/7
Milestones:      17/17
Tickets:         565/565
Ticket files:    49/49
Custom values:   2344/2344
Wiki edits:      308/308
Wiki files:      6/6

migrate project2:
---
Migrating components                     [******************************] 100%  
Migrating milestones                     [******************************] 100%  
Migrating tickets                        [******************************] 100%  
Migrating wiki                           [******************************] 100%  

Transform texts to textile format:
   in Wiki pages                         [******************************] 100%  
   in Issues                             [******************************] 100%  
   in Milestone descriptions             [******************************] 100%  

Components:      23/23
Milestones:      35/35
Tickets:         2203/2203
Ticket files:    263/263
Custom values:   4200/4200
Wiki edits:      4379/4379
Wiki files:      75/75