Check your language.phtml
If you are using flags instead of dropdown make sure you define the default language.
by using <?php if ($_lang->getCode() != 'default'): ?>
refer to complete code below
<?php if(count($this->getStores())>1): ?>
<div class="form-language">
<div class="langs-wrapper">
<?php foreach ($this->getStores() as $_lang): ?>
<?php if ($_lang->getCode() != 'default'): ?>
<?php $selected = $_lang->getId() == $this->getCurrentStoreId() ?>
<a class="lang-flag<?php $selected && print ' selected' ?>" href="<?php echo $_lang->getCurrentUrl() ?>">
<img src="<?php echo $this->getSkinUrl('images/flags/' . $_lang->getCode() . '.png');?>" alt="<?php echo $this->htmlEscape($_lang->getName()) ?>" height="16" width="24">
</a>
<?php endif;?>
<?php endforeach ?>
</div>
</div>
<?php endif;?>