CheckboxSelectMultiple widget Django renders already collapsed in form - django

Question

I am trying to create a form where you can enter the language or languages. I want to use a CheckboxSelectMultiple widget, but it renders already collapsed in the form:
The form with already collapsed select
How can I fix this?
forms.py:
class TweetForm(forms.ModelForm):
class Meta:
model = TweetSearch
fields = ['search_term', 'query_type', 'start_date', 'end_date', 'language', 'country', 'tweet_count']
widgets = {
'search_term': forms.TextInput(attrs={'class': 'form-control', 'placeholder': 'Search...'}),
'query_type': forms.Select(attrs={'class': 'form-control'}),
'tweet_count': forms.NumberInput(attrs={'class': 'form-control', 'placeholder': 'Number of tweets'}),
'start_date': DateTimePickerInput(attrs={'class': 'form-control', 'placeholder': 'From'}),
'end_date': DateTimePickerInput(attrs={'class': 'form-control', 'placeholder': 'Till'}),
'language': forms.CheckboxSelectMultiple(attrs={'class':'form-control'})
}
html:
<div id="searchcontainer">
<div class="card w-50 text-center mx-auto mt-8" id="searchcard">
<div class="card-header">
Search
</div>
<div class="card-body">
<h5 class="card-title">Search for tweets</h5>
<form action="" method="POST">
{% csrf_token %}
<div class="form-row">
<div class="form-group col-md-4">
{{form.search_term}}
</div>
<div class="form-group col-md-4">
{{form.query_type}}
</div>
<div class="form-group col-md-4">
{{form.tweet_count}}
</div>
</div>
<div class="form-row">
<div class="form-group col-md-6">
{{form.start_date}}
</div>
<div class="form-group col-md-6">
{{form.end_date}}
</div>
</div>
<div class="form-row">
{{form.language}}
</div>
<input class="btn btn-primary mb-2" type="submit">
</form>
</div>
</div>