Hi. Maybe you can tell us how did you resolved your issue (for other people in the community)?

For Odoo 8, a module displaying countries flags in the top navigation bar exists: https://www.odoo.com/apps/modules/8.0/website_lang_flags/ (but it must be debug).

[SOLUTION]

You have to replace the following code in automatic footer

<li groups="base.group_website_publisher">

    <t t-set="url_return" t-value="url_for('', '[lang]') + '?' + keep_query()"/>

    <a t-attf-href="/web#action=base.action_view_base_language_install&amp;website_id=#{website.id}&amp;url_return=#{url_return}">

        <i class="fa fa-plus-circle"/>

        Add a language...

    </a>

</li>

with this code:

 <t t-if="lang_name == ' Deutsch'">

    <img alt="german" src="/theme_teamdoc/static/src/img/kastrup_genberg/ger.png"/>

</t>

<t t-if="lang_name == 'English'">

    <img alt="english" src="/theme_teamdoc/static/src/img/kastrup_genberg/uk.png"/>

</t>

As you see I wrote a t-if with the language name (lang_name="theLanguageIwant") and in this t-tag I inserted the image of the flag.