Page to Show Lack of Translation

Ok, this was partly my fault because of a wrong setting in the Site Configuration/Multilingual System! I set this now to "Current language and no language" and now the german pages disappear when I click on the english flag and vice versa!

But not always! Here's the remaining problem explained better I hope:

Step 1:
I click on the german flag in the language switcher. Now my menu is:
A
B
C

C show a language neutral page, A is german without translation, B is english with english translation "B-eng".

Step 2:
I click on C and watch the page C. Now I click on the english flag in the language switcher block. My menu becomes

B-Eng
C

Thats fine!

Step 3:
Now I switch back to german and click on A, i.e. I watch the german page A and have menu
A
B
C

Step 4:
While wachting page A, I click on the english flag again. Now nothing changes. My menu still is
A
B
C
but the path changes from http://bla/node/31 to http://bla/en/node/31, although still showing the german page A.

Step 5:
Now I click on C. And at this moment, the menu changes to
B-Eng
C

I think this is not a good solution. I understand that in Step 4 drupal keeps showing page A, because there is no english translation of it and instead of showing a 404 error or sth. it keeps showing the german page.

BUT in step 4 the menu should change immediately when clicking on the english flag. That should not be delayed until I click on menu entry C in step 5.

I guess thats not the same behaviour. When I'm at a page that is only in English and not in German and click on the german flag, nothing changes. Not even the menu. It stays all the same with all english-only entries. Only when I then click on the menu at a page that has both languages, then all of a sudden the menu switches all its entries from english to german.

Your problem that after clicking on the Czech button you get the Czech-only menu items, but the English-only items also remain in the menu, is likely related to the settings. Go to Site Configuration/Multilingual System and chose "Current language and no language". Then you will only have either the Czech-only or the English-only menue entries.

But my problem is that the menu doesn't change when I click on the language flag while I'm at a page that has a language but no translation to the other language.

Hmm, the behaviour here has indeed changed. After I configured a lot and reinstalled the i18n module for other reasons, it behaves exactly as you describe which is still different from what I was seeing before.
I think it would be a nice feature for i18n if one could define a default error page that is in the language for which no translation exists and would show sth. like

"There is no translation for this page yet. Please create a translation of set the page to "language neutral" to view it with the current language selection"

If such a page existed and was linked from the language flag, the menu would switch the right way, just like if a translation existed. And such a page would be helpful also, I guess.

I guess it should not be that hard. I was able to hack that into my own little language switcher block that I created to show switchers for all but the current language (see http://drupal.org/node/242646), but of course this is just a dirty hack that works for me with my i18n and my language settings. I've no idea how general that is.
I just send the user to a predefined error page when no translation exists. You should create such a page for all languages and give it the same alias, see below. Then it works with my language settings of "Path prefix only". Since the error page is in the right language, the menu switches as expected.

Someonw with better knowledge should be able to make the href path configurable, for instance, or realize the dynamic solution (sketched in the comments below). But maybe this snippet helps some people for now.

  // shows language selection links and/or flags for all but the
  // current language. In contrast to the language switcher
  // block, it will send the user to a "translation does not exist"
  // page if a page with a language is missing a translation.

  // this is copy&paste from locale_block in locale.module
  $languages = language_list('enabled');
  $links = array();
  foreach ($languages[1] as $language) {
    $links[$language->language] = array(
        'href'       => $_GET['q'],
        'title'      => $language->native,
        'language'   => $language,
        'attributes' => array('class' => 'language-link'),
        );
  }

  // this adds the real paths, i.e. if we are on a german page,
  // the british flag will point to en/english_alias instead of 
  // en/node_with_german_content
  translation_translation_link_alter($links, $_GET['q']);

  // This one adds extended languages, i.e. those that are not enabled.
  // Disable if you want only flags for enabled languages.
  i18n_translation_link_alter($links, $_GET['q']);
  


  // now add or replace text links by flags, according to your i18n settings.
  //if (function_exists('languageicons_translation_link_alter'))
    languageicons_translation_link_alter($links, $_GET['q']);  

  // Or do your own stuff, e.g. set the flags and no lang names,
  // no matter what the i18n icon settings say.
  //if ($icon = theme('languageicons_icon', $language, NULL)) {
  //   $links[$language->language]['title'] = theme('languageicons_place', $link['title'], $icon);
  //   $links[$language->language]['html'] = TRUE;           
  //}
  
  // for pages that are not language neutral but have no translation for
  // a certain language, clicking the flag/link of that language will
  // change the current language, but the page and the menu will just stay.
  // When you chose another page afterwards it will still display in the old
  // language, but with a lang prefix of the new language (if you are using
  // language prefixes in the node path). And although the pages continue to
  // show e.g. in german, the current language is british so that you will see
  // a german flag while on a german page. Weired.
  // We correct that by sending the user to a "There is no translation for that
  // language" page. What you have to do: Create such a page for every language
  // that you have, and give *all* of those pages the same alias "no_translation".
  // With i18n in use and language setting "Path prefix only", this will send
  // you to de/no_translation, en/no_translatio etc. automatically. 
  // No other settings tested, but you can manipulate the link as you like,
  // e.g. give your translations aliases like "no_translation_en" etc. and
  // set the href to no_translation_$links[$langcode]['language']->language.
  // NOTE: the following code has only been tested with "Path prefix only" and
  // with i18n enabled.
  // Drawback: when you click the language flag while on the error page, you
  // are not redirected to the page you came from, but to the translation of
  // the error page. You could give your error page a little button to go back
  // to the former page using javascript or the referrer variable.
  // A way to solve this would be to dynamically generate a page when clicking the
  // language flag, configure this page as translation of the node you just viewed and
  // let the newly generated page display the error text. Shouldn't be that hard
  // for people with better drupal knowledge.
  $current = i18n_get_lang();
  $current_link=$links[$current];

  if ( arg(0) == 'node' && is_numeric(arg(1)) ) {
    $node = node_load(arg(1));
  }
  // just work on pages that are not language neutral
  if (!empty($node->language)) {
    foreach ($links as $langcode => $link) {
      # if languages are different, but the hrefs are equal, than we have no translation
      if (($links[$langcode]['language']->language != $current) &&
          ($links[$langcode]['href'] == $current_link['href'])){
        // for people with more knowledge, you could make the target href
        // configurable by some menue settings for your own module...
        $links[$langcode]['href']='no_translation';
      }
    }
  }

  // remove the current language again. We cannot do that
  // earlier because i18n_translation_link_alter would add it
  // again, thinking it was an extendeg language because it
  // was not yet contained in $links. If you don't use 
  // i18n_translation_link_alter, you can also make a case distinction
  // in the foreach loop
  $current = i18n_get_lang();
  unset($links[$current]);

  // format as you like, e.g.
  echo theme('links', $links, array());

This does not seem to work in Drupal 6.14

Fatal error: Call to undefined function i18n_translation_link_alter(