Update Devise user with association to 'Language' model - ruby-on-rails

Question

Building a Rails app using devise. The user can edit all the information on their profile page (name, description etc.) inside devise/edit.html.erb. The user model has an association to language model. I want the user to be able to pick their own language when editing their profile from a f.select. How do I make this happen?
Thanks in advance.
Edit.html.erb:
<div class="panel-body">
<div class="panel-body">
<%= form_for(resource, as: resource_name, url: registration_path(resource_name), html: { method: :put }) do |f| %>
<%= devise_error_messages! %>
<div>
<div class="form-group">
<%= f.label :coach_id %>
<%= f.select(:coach_id, User.where('is_coach = ?', true).pluck(:name, :id), {}, { :class => 'select2 form-control' }) %>
</div>
<div class="form-group">
<%= f.label :description %>
<%= f.text_area :description, class: 'form-control', rows: '5' %>
</div>
<div class="form-group">
<%= f.label :facebook %>
<%= f.text_field :facebook, class: 'form-control' %>
</div>
<div class="form-group">
<%= f.label :twitter %>
<%= f.text_field :twitter, class: 'form-control' %>
</div>
<div class="form-group">
<%= f.label :image %>
<%= f.file_field :image, class: 'form-control' %>
</div>
<div class="form-group">
<%= f.label :header_image %>
<%= f.file_field :header_image, class: 'form-control' %>
</div>
</div>
<br>
<%= f.submit 'Update Settings', class: 'btn btn-success' %>
<% end %>
</div>
</div>
Schema:
create_table "users", force: :cascade do |t|
t.string "email", default: "", null: false
t.string "encrypted_password", default: "", null: false
t.string "reset_password_token"
t.datetime "reset_password_sent_at"
t.datetime "remember_created_at"
t.integer "sign_in_count", default: 0, null: false
t.datetime "current_sign_in_at"
t.datetime "last_sign_in_at"
t.inet "current_sign_in_ip"
t.inet "last_sign_in_ip"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
t.boolean "admin", default: false
t.boolean "is_coach", default: false
t.text "description"
t.string "image_uid"
t.string "header_image_uid"
t.string "facebook"
t.string "twitter"
t.boolean "featured"
t.integer "coach_id"
t.string "name"
t.index ["email"], name: "index_users_on_email", unique: true, using: :btree
t.index ["reset_password_token"], name: "index_users_on_reset_password_token", unique: true, using: :btree
end
create_table "languages", force: :cascade do |t|
t.string "language_code"
t.integer "user_id"
t.index ["user_id"], name: "index_languages_on_user_id", using: :btree
end
create_table "languages_users", force: :cascade do |t|
t.integer "user_id"
t.integer "language_id"
t.index ["language_id"], name: "index_languages_users_on_language_id", using: :btree
t.index ["user_id"], name: "index_languages_users_on_user_id", using: :btree
end
User
has_and_belongs_to_many :languages
Language
has_and_belongs_to_many :users