Set parent nav to active
You need to get all possible translations of your entry slug to do a thorough comparison.

This is only possible with additional DB queries (ElementCriteriaModels) for each of your navigation items and each of your installed locales, if you don't want to hardcode the values into your template.

Because your navigation probably doesn't change that often, I'd do it anyways and simply wrap the whole navigation in {% cache %} tags with a really long invalidation time (it does get updated if anything is changed within the tags though!).

{% cache for 3 years %}
{% for naviItem in navi %}

    {# Get the relevant URL segment #}
    {% set segment = craft.request.segment(1) %}

    {# Get all possible translations of the entry slug #}
    {% set enSlug = craft.entries.id(naviItem.id).locale('en').first().uri %}
    {% set frSlug = craft.entries.id(naviItem.id).locale('fr').first().uri %}
    {% set deSlug = craft.entries.id(naviItem.id).locale('de').first().uri %}

    {# Define a variable `activeClass` if the URL segment matches one of the slug translations #}
    {% if segment == enSlug or segment == frSlug or segment == deSlug %}
        {% set activeClass = ' active' %}
    {% endif %}

    &lt;li&gt;
        {# If the `activeClass` var is set, add its value to the link's classes #}
        &lt;a href="{{ naviItem.url }}" class="defaultClasses{{ activeClass ? activeClass }}"&gt;
            {{ naviItem.naviTitel }}
        &lt;/a&gt;
    &lt;/li&gt;

{% endfor %}
{% endcache %}